Production and Costs | CBSE Class 11 Economics Notes

This note covers production functions, efficient input use, the short run and long run, total, average and marginal product, variable proportions, returns to scale, fixed and variable costs, average and marginal costs, and the relationships between production and cost curves.

What do production and a production function mean?

Production transforms inputs into output. Inputs are resources used in production, such as labour, machines, land and raw materials. Output is the good or service produced. A firm is a producer that combines inputs to produce this output.

A tailor uses a sewing machine, cloth, thread and labour to make shirts. A farmer combines land, labour, a tractor, seed, fertiliser and water to produce wheat. Production also includes services: a rickshaw puller produces rides and a domestic helper produces cleaning services.

What assumptions simplify the analysis?

In the simple model, production is instantaneous: no time elapses between combining inputs and producing output. The cost of production is the payment needed to acquire inputs; revenue is what the firm earns by selling output.

Profit is revenue minus cost. The firm is assumed to aim at the maximum profit it can earn. Understanding how inputs produce output, and what those inputs cost, helps explain the firm's output decision.

Definition: A production function gives the maximum output obtainable from different combinations of inputs, for a given technology.

Factors of production are the inputs used by a firm. In a two-factor model, let q denote maximum output, L the quantity of labour and K the quantity of capital. Capital here is a productive input, such as machinery. The symbol f denotes the functional relationship.

q = f(L, K)

A production function concerns efficient use: no more output can be obtained from the same inputs. It is defined for a given technology, meaning the technological knowledge available for production. An improvement in technology raises obtainable output and gives a new production function.

Worked example 1. In the wheat example, q = K × L, where q is wheat output in tonnes, K is land in hectares and L is hours of work per day. Find output with 1 hectare and 2 hours of labour per day.

Answer: q = 1 × 2 = 2 tonnes of wheat. In this particular example K represents land; in the general two-factor model it represents capital.

How do we read a production schedule and an isoquant?

A production schedule lists output for particular combinations of inputs. In the following schedule, rows identify labour and columns identify capital. Each entry is the maximum output obtainable from that combination. Reading across a row varies capital while holding labour constant.

Table: Production function, with output in units

With 1 unit of each input, maximum output is 1 unit. With 2 units of each, it is 10 units. With 3 units of labour and 2 units of capital, it is 18 units. In this example, both inputs are necessary: zero of either gives zero output.

How can different input combinations give equal output?

An isoquant is the set of input combinations yielding the same maximum possible output. Each isoquant is labelled by its output level. In the schedule, 10 units can be produced with labour-capital combinations (4, 1), (2, 2) and (1, 4).

These combinations belong to the same isoquant. Similarly, 50 units can be obtained from combinations (6, 3), (4, 4) and (3, 6). Equal output does not mean equal quantities of each input: a firm can combine more of one input with less of the other.

For an isoquant graph, labour is on the horizontal axis and capital on the vertical axis. When each input's marginal product, meaning the output change per unit change in that input with the other fixed, is positive, isoquants slope downwards. Maintaining output while increasing one input then requires reducing the other.

Moving down a column of the schedule answers a different question: how output changes when labour varies and capital stays fixed. Thus the same production schedule helps examine both alternative ways of obtaining one output and output changes with one input fixed.

How do the short run and long run differ?

The short run is a period in which at least one factor cannot be varied. That input is a fixed factor. An input whose quantity can be changed is a variable factor. With one factor fixed, changes in output require changes in the variable factor.

For the production schedule above, suppose capital is fixed at 4 units. The firm can change labour and move down that capital column. This gives output levels of 0, 10, 24, 40, 50, 56 and 57 units as labour increases from 0 to 6 units.

What makes a period the long run?

In the long run, all factors can be varied. A firm can change labour and capital simultaneously, and there is no fixed factor. The distinction depends on the flexibility of inputs rather than a universally prescribed number of days, months or years.

For a particular production process, the long run generally refers to a longer period than the short run. Different production processes may have different long-run periods. The relevant question is whether all inputs can be changed in the period being considered.

This distinction also explains why different production relationships are studied separately. Changing labour with capital fixed changes the ratio between inputs. Increasing both inputs proportionately is a different exercise, possible in the long run, and is examined through returns to scale, the output response to proportionate increases in all inputs.

How are total, average and marginal product calculated?

The relationship between a variable input and output, with other inputs constant, is often referred to as total product (TP). It is also sometimes called total physical product or total return to the variable input. With capital fixed, a labour schedule shows the output from each employment level.

Average product (AP) is output per unit of variable input. Marginal product (MP) is the change in output per unit change in that input, holding all other inputs constant. Write APₗ and MPₗ for average and marginal product of labour.

APₗ = TP / L

The symbol Δ means a change in a variable. Thus ΔTP is the change in total product and ΔL is the change in labour employed.

MPₗ = ΔTP / ΔL

When labour increases by one unit, marginal product is the new total product minus the previous total product. The following schedule uses capital fixed at 4 units. A dash indicates an undefined value at zero labour employment.

How do the three measures connect?

The sum of marginal products of successive input units gives total product. Average product is the average of these marginal products up to the employment level concerned. Average and marginal products are often also called average and marginal returns to the variable input.

Worked example 2. With capital fixed at 4 units, total product is 10 at 1 unit of labour and 24 at 2 units. Calculate the marginal product of the second unit and average product at 2 units of labour.

Answer: MPₗ = (24 − 10) / (2 − 1) = 14 units of output per additional labour unit. APₗ = 24 / 2 = 12 units of output per labour unit.

At zero employment, marginal product is undefined because inputs cannot take negative values. Average product at zero employment is also undefined: output cannot be divided by zero labour. These undefined entries should not be interpreted as zero product values.

Why does marginal product first rise and then fall?

Definition: The law of variable proportions describes marginal product initially rising with the employment of an input and falling after a certain employment level, while other inputs remain fixed.

The tendency is also discussed as the law of diminishing marginal product. Its explanation lies in factor proportions, the ratio in which inputs are combined. Keeping one factor fixed and increasing another changes this ratio as production expands.

How does the fixed-land example explain the law?

Consider a farmer with 4 hectares of land who can choose the amount of labour employed. With only one worker, there is too much land for that worker to cultivate alone. Adding workers initially makes the combination of labour and land more suitable for production.

1. Land remains fixed while the number of workers increases, so labour per unit of land rises.
2. Initially, the factor proportions become more suitable, and each additional worker contributes a larger addition to total output.
3. When the fourth worker is hired in this example, the land begins to become crowded.
4. Workers then have insufficient land to work efficiently, and the addition to output made by each further worker becomes smaller.

The product schedule shows marginal products of 10, 14 and 16 for the first three labour units. They then fall to 10, 6 and 1. The largest marginal product in this schedule is therefore associated with the third labour unit.

Falling marginal product should be distinguished from falling total product. In this schedule, each marginal product remains positive. Total product therefore continues to rise, but the later increments become smaller. The sixth labour unit still adds output, although much less than the third.

The condition that another input remains fixed is central to the explanation. If all inputs increase in the same proportion, their proportions do not change. That situation belongs to returns to scale, rather than this explanation based on a changing input ratio.

How are the total, average and marginal product curves related?

A total product curve plots the variable input against output, with other inputs fixed. Labour is measured horizontally and output vertically. For the illustrated typical firm, total product slopes upwards, showing the different maximum output levels obtainable from different labour quantities.

The curve rises from origin O, first steepening and then flattening. A vertical guide at labour quantity L meets the curve at output q₁, the indicated output level. A horizontal guide links this point to the output axis.

See Fig. 3.1 in your NCERT textbook

Why are average and marginal product inverse U-shaped?

The law of variable proportions gives the MP curve an inverse U-shape: it first rises and then falls. The AP curve is also inverse U-shaped, but its movement depends on the relationship between the marginal contribution and the existing average.

1. For the first unit of variable input, average product and marginal product are equal.
2. As marginal product rises, average product also rises, but by less than marginal product.
3. After marginal product begins falling, average product continues rising while marginal product remains above it.
4. Once marginal product falls below average product, average product also falls.

The MP curve therefore crosses the AP curve from above at the maximum of AP. A falling MP is compatible with a rising AP when the extra input's contribution is still greater than the average contribution of the inputs already employed.

Labour is on the horizontal axis and output on the vertical axis. The MPₗ curve peaks before the APₗ curve. They meet at P, the maximum of APₗ, above the marked labour quantity L.

See Fig. 3.2 in your NCERT textbook

To the left of the marked labour quantity in this graph, AP is rising and MP is above it. To the right, AP is falling and MP is below it. The intersection identifies maximum average product, rather than maximum marginal product.

What happens when all inputs increase in the same proportion?

Returns to scale describe the output response when all inputs increase proportionately. This is a long-run exercise because all factors must be variable. Unlike the law of variable proportions, it keeps the input ratio unchanged while expanding the scale of production.

How can returns to scale be written mathematically?

Let x₁ and x₂ denote the quantities of factor 1 and factor 2. Let t be the common multiplier applied to both inputs, with t > 1. Initial output is f(x₁, x₂), while output after expansion is f(tx₁, tx₂).

• CRS: f(tx₁, tx₂) = t × f(x₁, x₂).
• IRS: f(tx₁, tx₂) > t × f(x₁, x₂).
• DRS: f(tx₁, tx₂) < t × f(x₁, x₂).

These tests compare the new output with the original output multiplied by t. They do not compare output with the number of inputs in isolation. Both factors must have been increased by the same multiplier for this comparison to describe returns to scale.

What is the Cobb-Douglas example?

A Cobb-Douglas production function can be written q = x₁ᵅ × x₂ᵝ, where α and β are constant exponents, shown as superscripts. Multiplying both inputs by t multiplies output by t raised to the power α + β.

If α + β = 1, output increases t times and the function has CRS. If α + β > 1, it has IRS. If α + β < 1, it has DRS. The sum of the exponents therefore determines the type of returns in this example.

How does a firm choose inputs and calculate total costs?

A given output can typically be produced using more than one input combination. For example, the production schedule allows 50 output units with labour-capital combinations (6, 3), (4, 4) and (3, 6). Choosing between them requires knowing the prices of the inputs.

Definition: A cost function describes the least cost of producing each output level, given factor prices and technology.

With input prices given, the firm chooses the least expensive combination that produces its desired output. A production function concerns technically attainable output; a cost function also considers the payments required to obtain the inputs used for that output.

What are fixed, variable and total costs?

Total fixed cost (TFC) is the cost of employing fixed inputs. It remains unchanged as short-run output changes and must be incurred even when output is zero. Total variable cost (TVC) is the cost of employing variable inputs.

Total cost (TC) is the sum of these two components. In the cost formulas, q continues to denote the quantity of output produced.

TC = TVC + TFC

Producing no output requires no variable inputs, so TVC is zero at zero output. TC then equals TFC. As output increases, more variable inputs are required, causing TVC and TC to increase. TFC does not change with output in the short run.

Output is on the horizontal axis and costs on the vertical axis. TFC is horizontal; TVC starts at origin O; TC starts above O. At marked output q₁, the labels c₁, c₂ and c₃ indicate TFC, TVC and TC respectively.

See Fig. 3.3 in your NCERT textbook

TC is the vertical sum of TFC and TVC. Its vertical distance above TVC is the fixed cost at each output level. This graph separates the part of expenditure that varies with production from the part that remains fixed.

How do we calculate average and marginal costs from a schedule?

Short-run average cost (SAC) is total cost per unit of output. Average variable cost (AVC) is variable cost per output unit, and average fixed cost (AFC) is fixed cost per output unit. These measures divide the relevant total by q.

SAC = TC / q

AVC = TVC / q

AFC = TFC / q

SAC = AVC + AFC

Short-run marginal cost (SMC) is the change in total cost per unit change in output. It measures the additional cost associated with expanding production, rather than the average cost of all output already produced.

SMC = ΔTC / Δq

Here ΔTC means the change in total cost and Δq the change in output. Because fixed cost cannot change in the short run, the change in TC is entirely a change in TVC. For a one-unit output increase, SMC equals that increase in TVC.

What does the numerical cost schedule show?

All cost entries below are in rupees, written Rs. Output is measured in units. Dashes mark undefined entries at zero output.

Worked example 3. At 2 output units, TFC is Rs 20 and TVC is Rs 18. Find TC, AFC, AVC and SAC.

Answer: TC = 20 + 18 = Rs 38. AFC = 20 / 2 = Rs 10; AVC = 18 / 2 = Rs 9; SAC = 38 / 2 = Rs 19. Thus SAC also equals Rs 10 + Rs 9.

Worked example 4. TC is Rs 49 at 4 output units and Rs 53 at 5 units. Calculate the marginal cost of the fifth unit.

Answer: SMC = (53 − 49) / (5 − 4) = Rs 4. The extra unit raises total cost by Rs 4, entirely through variable cost.

For successive single units, the sum of marginal costs up to an output level gives TVC at that level. AVC is the average of those marginal costs. At zero output, the average costs and marginal cost are undefined.

Why does average fixed cost fall as output rises?

Average fixed cost divides a constant total fixed cost by changing output. As positive output rises, AFC falls. The same fixed expenditure is spread over more units. In the cost schedule, TFC stays at Rs 20 throughout, while AFC falls as output increases.

When positive output is very close to zero, AFC is arbitrarily large. As output moves towards infinity, AFC moves towards zero. The AFC curve is a rectangular hyperbola: multiplying any positive output by its corresponding AFC gives the same constant, TFC.

TFC = AFC × q

How do a rectangle and a ray show costs?

Output is horizontal and cost vertical. The downward-sloping AFC curve contains point C at output q₁. F marks the corresponding AFC on the cost axis. The rectangle OFCq₁ has area equal to total fixed cost, with O denoting the origin.

See Fig. 3.4 in your NCERT textbook

The rectangle's width is output and its height is cost per unit. Multiplying them gives total fixed cost. This is a graphical reading of AFC × q, rather than a separate rule for calculating costs.

The same average can be read from the total fixed cost graph. At a selected output, divide the height of the horizontal TFC line by the corresponding horizontal distance from the origin. This is the slope of the ray joining the origin to that point.

A related relationship applies to variable cost: AVC multiplied by output gives TVC. On an AVC graph, the rectangle with output as width and AVC as height represents TVC. On a TVC graph, the slope of the ray from the origin gives AVC.

These constructions keep total and average costs distinct. A height on the total cost graph measures a total expenditure; dividing that height by output gives an expenditure per unit. A rectangle under an average-cost height reverses this calculation.

Why are short-run average and marginal cost curves U-shaped?

The SMC curve reflects the law of variable proportions. Initially, marginal product rises, so producing each additional unit of output requires less additional variable input. With the factor price given, the additional cost of output falls.

After a certain point, marginal product falls. More additional input is then required for each extra output unit, and SMC rises. The typical SMC curve is therefore U-shaped. The area under this curve up to a given output measures TVC at that output.

How does marginal cost affect average variable cost?

1. For the first output unit, SMC and AVC are equal.
2. As SMC initially falls, AVC also falls, but by less, because it averages the marginal costs.
3. AVC continues falling after SMC begins rising, provided SMC remains below AVC.
4. When SMC exceeds AVC, AVC rises; SMC therefore cuts AVC from below at AVC's minimum.

The resulting AVC curve is U-shaped. A rise in marginal cost does not immediately imply a rise in average variable cost. What matters for the average is whether the additional cost is below or above the existing average.

Why does average total cost reach its minimum later?

SAC equals AVC plus AFC. Initially, both components fall, so SAC falls. When AVC begins rising, AFC is still falling. SAC continues falling while the fall in AFC exceeds the rise in AVC, and rises once the increase in AVC becomes larger.

The SAC curve is therefore U-shaped and lies above AVC. Their vertical difference equals AFC. SAC reaches its minimum at a larger output than AVC. SMC is below SAC while SAC falls and above SAC while SAC rises.

Cost is vertical and output horizontal. SMC cuts AVC from below at P, its minimum at output q₁. SMC then cuts SAC from below at S, its minimum at output q₂. Here q₂ is to the right of q₁.

See Fig. 3.8 in your NCERT textbook

The same marginal-average rule explains both intersections. Marginal cost below an average pulls that average down; marginal cost above it pulls the average up. Equality at the minimum marks the change between falling and rising average cost.

How do long-run costs depend on returns to scale?

All inputs are variable in the long run, so there are no fixed costs. Total cost and total variable cost coincide. Long-run average cost (LRAC) is cost per unit of output, while long-run marginal cost (LRMC) is the change in total cost per unit change in output.

LRAC = TC / q

LRMC = ΔTC / Δq

For output changing in single units, LRMC is the difference between total cost at the new output and total cost at the previous output. In the long run, the sum of successive marginal costs up to an output level gives TC at that level.

How do the three returns affect average cost?

Under increasing returns to scale, a proportional output increase requires a smaller proportional input increase. With input prices given, cost rises by less than output, so LRAC falls. To double output, for example, inputs and their cost need to rise by less than double.

Under decreasing returns to scale, a proportional increase in output requires a larger proportional increase in inputs. Cost therefore rises more than proportionately, and LRAC rises. Under constant returns to scale, inputs and output rise proportionately, so average cost stays constant.

It is argued that a typical firm initially experiences IRS, followed by CRS and then DRS. Accordingly, the typical LRAC curve is U-shaped. Its falling part corresponds to IRS, its rising part to DRS, and its minimum to CRS.

Cost is on the vertical axis and output on the horizontal axis. LRMC crosses LRAC from below at M, the minimum of LRAC. A vertical guide connects M to the marked output q₁.

See Fig. 3.9 in your NCERT textbook

For the first output unit, LRMC and LRAC are equal. LRMC is below LRAC while LRAC falls and above it while LRAC rises. The typical LRMC curve is also U-shaped and cuts LRAC from below at its minimum.

Glossary

• Production — The process of transforming inputs into output, including goods and services.
• Production function — A relationship showing maximum output obtainable from input combinations for a given technology.
• Isoquant — A set of input combinations yielding the same maximum possible output level.
• Short run — A period in which at least one production factor cannot be varied.
• Long run — A period in which all factors of production can be varied.
• Total product — The relationship between a variable input and output with other inputs held constant.
• Average product — Output per unit of the variable input employed in production.
• Marginal product — Change in output per unit change in one input, holding other inputs constant.
• Factor proportions — The ratio in which inputs are combined to produce output.
• Returns to scale — The output response when all production inputs increase in the same proportion.
• Cost function — The least cost of producing each output level, given input prices and technology.
• Total fixed cost — The cost of employing fixed inputs, unchanged by short-run output variations.
• Total variable cost — The cost of employing variable inputs, changing as production changes.
• Average cost — Total cost divided by the quantity of output the firm produces.
• Marginal cost — The change in total cost per unit change in output produced.

Common errors and misconceptions

• Misconception: A production function shows any output obtained from inputs. Correct: It shows the maximum obtainable output for the given inputs and technology.
• Misconception: The short run is a fixed number of months. Correct: It is defined by at least one input being fixed; adjustment periods differ across production processes.
• Misconception: Falling marginal product necessarily means falling total product. Correct: In the product schedule, marginal product falls but stays positive, so total product continues rising.
• Misconception: Average product starts falling as soon as marginal product falls. Correct: Average product continues rising while marginal product remains above it.
• Misconception: Variable proportions and returns to scale change inputs in the same way. Correct: The former keeps another input fixed; the latter increases all inputs proportionately.
• Misconception: Zero output means zero total cost in the short run. Correct: Total variable cost is zero, but total cost equals the fixed cost.
• Misconception: Falling AFC means falling TFC. Correct: AFC falls because unchanged fixed cost is divided among more output units.
• Misconception: Short-run marginal costs add up to total cost. Correct: They add up to total variable cost; fixed cost must be added to obtain total cost.

Exam-style questions with model answers

Q1. Define a production function and explain the role of technology. [2 marks]

1. A production function shows the maximum output a firm can obtain from different combinations of inputs, using them efficiently.
2. It is defined for a given technology. Improved technology raises obtainable output from input combinations and gives a new production function.

Q2. Distinguish between the short run and the long run. [3 marks]

1. In the short run, at least one factor cannot be varied and is a fixed factor. The firm changes output by varying the other input.
2. In the long run, all factors can be varied. Labour and capital may change simultaneously, and there is no fixed factor.
3. The distinction concerns input flexibility, not a universal number of days or months. Different production processes may have different long-run periods.

Q3. With capital fixed at 4 units, total product is 10 units at 1 unit of labour and 24 units at 2 units of labour. Calculate the second labour unit's marginal product and average product at 2 labour units. [2 marks]

1. Marginal product of labour = change in output / change in labour = (24 − 10) / (2 − 1) = 14 output units per additional labour unit.
2. Average product of labour = total product / labour = 24 / 2 = 12 output units per labour unit.

Q4. Explain the law of variable proportions using a farmer with 4 hectares of fixed land who starts with one worker and increases labour, with crowding beginning when the fourth worker is hired. [5 marks]

1. The law describes marginal product initially rising with the employment of a variable input and then falling beyond a certain level, while another input remains fixed.
2. Factor proportions mean the ratio of inputs used. Increasing labour while keeping land fixed changes these proportions by raising labour per unit of land.
3. With only one worker, there is too much land to cultivate alone. Adding workers initially makes the input combination more suitable for production.
4. During this initial phase, additional workers make increasingly large contributions to total output. The marginal product of labour therefore rises.
5. When the fourth worker is employed in this example, land becomes crowded. Workers have insufficient land to work efficiently, and each further worker adds less output.

Q5. At 2 units of output, a firm's total fixed cost is Rs 20 and its total variable cost is Rs 18. Calculate total cost, average fixed cost, average variable cost and short-run average cost. [4 marks]

1. Total cost combines fixed and variable costs: TC = TFC + TVC = 20 + 18 = Rs 38.
2. Average fixed cost spreads total fixed cost across output: AFC = total fixed cost / output = 20 / 2 = Rs 10 per unit.
3. Average variable cost divides variable cost by output: AVC = total variable cost / output = 18 / 2 = Rs 9 per unit.
4. Short-run average cost is total cost per unit: SAC = total cost / output = 38 / 2 = Rs 19, also equal to AFC + AVC.

Q6. A firm's total cost is Rs 49 at 4 output units and Rs 53 at 5 output units. Calculate the marginal cost of the fifth unit and explain why it also equals the change in variable cost. [3 marks]

1. The increase in total cost is Rs 53 − Rs 49 = Rs 4, while the increase in output is 5 − 4 = 1 unit.
2. Short-run marginal cost equals change in total cost divided by change in output. The fifth unit's marginal cost is therefore Rs 4 / 1 = Rs 4.
3. Fixed cost remains unchanged in the short run. Consequently, the entire Rs 4 increase in total cost is an increase in total variable cost.

Q7. Explain why the short-run marginal cost curve is U-shaped and cuts the average variable cost curve at its minimum. Assume the factor price is given. [5 marks]

1. Initially, marginal product rises. Producing each extra output unit therefore requires less additional variable input, so its additional cost falls at the given factor price.
2. After a certain employment level, marginal product falls. Extra output then requires more additional input, raising marginal cost. These changes produce the U-shaped marginal cost curve.
3. Average variable cost is the average of successive marginal costs. When marginal cost is below this average, the additional unit pulls average variable cost down.
4. Average variable cost can continue falling after marginal cost begins rising, provided marginal cost remains below it. Once marginal cost exceeds the average, average variable cost rises.
5. Marginal cost therefore crosses average variable cost from below at its minimum, where the average changes from falling to rising.

Q8. Explain why average fixed cost falls and describe the shape of its curve. [3 marks]

1. Average fixed cost is total fixed cost divided by output. In the short run, total fixed cost stays unchanged when the firm changes its output.
2. As positive output rises, that constant cost is divided among more units, so average fixed cost falls. Multiplying output by its corresponding average fixed cost still gives total fixed cost.
3. The curve is a downward-sloping rectangular hyperbola. Average fixed cost is arbitrarily large near zero positive output and approaches zero as output tends towards infinity.

Key takeaways

• A production function links input combinations to maximum obtainable output for a given technology and assumes efficient input use.
• The short run has at least one fixed input; in the long run, all production inputs can be varied.
• Average product is output per input unit; marginal product measures the output change caused by an input change.
• Marginal product first rises and then falls under variable proportions, as the combination of fixed and variable inputs changes.
• The marginal product curve crosses average product from above at the maximum point of the average product curve.
• Total cost equals fixed plus variable cost, while average cost equals average fixed plus average variable cost.
• Short-run marginal cost cuts average variable cost and short-run average cost from below at their respective minimum points.
• With input prices given, increasing returns to scale lower long-run average cost, while decreasing returns raise it.

Test yourself

What changes the production function when input combinations remain available?

An improvement in technology raises the maximum output obtainable from input combinations, giving a new production function.

What does an isoquant represent?

It represents all input combinations that yield the same maximum possible level of output.

Why should the short run not be defined as a fixed number of months?

The distinction depends on whether all inputs can vary. Different production processes may require different periods for such adjustment.

When can marginal product fall while average product still rises?

This happens while marginal product, although falling, remains greater than the prevailing average product.

What is total cost at zero output in the short run?

It equals total fixed cost because total variable cost is zero when no output is produced.

What does the area under the short-run marginal cost curve measure?

Up to a given output level, it measures total variable cost at that output level.

Where does short-run marginal cost cross short-run average cost?

It crosses from below at the minimum point of the short-run average cost curve.

Why are there no fixed costs in the long run?

All production inputs can be varied in the long run, so total cost and total variable cost coincide.