Microeconomics Quiz: Long Run Production Costs
20 questions · exam conditions
0:00
Long Run Production CostsQuestion 1 of 20

A new biotechnology firm requires a multi-million dollar, highly specialized fermentation tank to produce its product. The tank can service a wide range of production volumes with little change in its operating cost. This large, indivisible capital expenditure is a significant source of:

diseconomies of scale.
diminishing marginal returns.
constant returns to scale.
economies of scale.
← Back to quizzes

Microeconomics Quiz

Microeconomics Quiz: Long Run Production Costs

Practice Long Run Production Costs in Microeconomics with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Long Run Production Costs, giving you a quick way to practice the rules, question types, and explanations that matter most for Microeconomics.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

A new biotechnology firm requires a multi-million dollar, highly specialized fermentation tank to produce its product. The tank can service a wide range of production volumes with little change in its operating cost. This large, indivisible capital expenditure is a significant source of:

  1. diseconomies of scale.
  2. diminishing marginal returns.
  3. constant returns to scale.
  4. economies of scale. (correct answer)
Explanation: Indivisible inputs, like the specialized tank, lead to economies of scale. The large fixed cost of the equipment can be spread over a larger and larger quantity of output, causing the average cost per unit to fall as the production volume increases. This is a primary source of economies of scale, where long-run average costs decrease as output rises. Diminishing marginal returns is a short-run concept. Constant returns would imply average cost is flat, and diseconomies would imply it is rising.

Question 2

A firm operates in a perfectly competitive market where the current price is $25. The firm's long-run average cost is minimized at $20 per unit when producing 800 units. Currently, the firm produces 600 units with a long-run average cost of $22 per unit. Assuming the firm can adjust its scale of operation, what should the firm do to maximize long-run profits?

  1. Increase output beyond 800 units to maximize total revenue given the competitive price of $25
  2. Decrease output below 600 units to take advantage of economies of scale in the declining cost region
  3. Maintain current output of 600 units since marginal revenue equals marginal cost at this production level
  4. Increase output to 800 units and expand plant size to achieve minimum average cost of $20 per unit (correct answer)
Explanation: When you encounter long-run profit maximization in perfect competition, remember that firms should produce where they can earn the highest profit per unit while considering their ability to adjust all inputs, including plant size. In this scenario, the firm faces a market price of $25 and has flexibility to change its scale of operation. The key insight is that the firm's long-run average cost reaches its minimum of $20 at 800 units of output. At this production level, the firm would earn a profit of 5perunit(5 per unit (25 - $20), which is the maximum possible profit per unit given the cost structure. Currently producing 600 units at $22 per unit gives only 3profitperunit(3 profit per unit (25 - $22). Since the firm can adjust its scale, it should move to the most efficient production level. Option A is wrong because producing beyond 800 units would increase average costs above the minimum $20, reducing profit per unit despite higher total revenue. Option B misunderstands economies of scale—the firm is already experiencing them between 600 and 800 units, so reducing output would move away from the cost-minimizing scale. Option C incorrectly assumes the current position is optimal and confuses short-run thinking (marginal analysis) with long-run optimization where the firm can change its entire cost structure. The correct answer is D: increase output to 800 units and expand plant size to achieve minimum average cost. Study tip: In long-run perfect competition problems, always look for the output level that minimizes average cost—this maximizes profit per unit when firms can adjust their scale of operation.

Question 3

A firm's long-run average cost curve has a minimum point at an output of 1,000 units and a cost of $8 per unit. If the firm is currently producing 800 units at a long-run average cost of $10 per unit, and market price is $9, what can be concluded about the firm's production decision?

  1. The firm should increase output because marginal cost is below average cost at current production levels
  2. The firm should decrease output because it is experiencing diseconomies of scale at current production levels
  3. The firm should increase output because it can reduce average costs by moving toward the efficient scale (correct answer)
  4. The firm should maintain current output because marginal revenue equals marginal cost at this production level
Explanation: The firm is producing below its efficient scale (800 < 1,000 units) and experiencing higher average costs ($10 > $8) than at minimum efficient scale. By increasing output toward 1,000 units, the firm can reduce its long-run average cost, moving down the declining portion of the LRAC curve. Choice A is incorrect because we don't know the relationship between MC and AC at 800 units. Choice B is wrong because the firm is experiencing economies of scale, not diseconomies. Choice D is incorrect because we have no information about MR = MC.

Question 4

An increasing-cost industry in perfect competition experiences a permanent increase in demand. Compare the long-run equilibrium before and after the demand change in terms of market price, individual firm output, and number of firms.

  1. Price increases, individual firm output remains constant at efficient scale, number of firms increases to meet higher demand (correct answer)
  2. Price remains constant, individual firm output increases beyond efficient scale, number of firms increases slightly
  3. Price increases, individual firm output decreases below efficient scale, number of firms increases significantly
  4. Price decreases due to increased competition, individual firm output remains constant, number of firms increases substantially
Explanation: In an increasing-cost industry, higher industry output raises input costs, shifting individual firms' cost curves upward and resulting in a higher long-run equilibrium price. However, each individual firm still produces at its new minimum long-run average cost (efficient scale) in the new equilibrium. The number of firms increases to meet the higher demand. Choice B is wrong because price must rise in increasing-cost industries. Choice C incorrectly suggests firms produce below efficient scale. Choice D incorrectly suggests price decreases when input costs rise.

Question 5

In the long run, a firm's production exhibits economies of scale for output levels below 500 units, constant returns to scale between 500 and 800 units, and diseconomies of scale above 800 units. If the current market price is $12 and the firm's minimum long-run average cost is $10, occurring at 650 units, which statement is most accurate?

  1. The firm will produce 650 units and earn economic profits of $2 per unit in long-run equilibrium
  2. The firm will produce somewhere between 500-800 units, with exact output determined by marginal revenue equals marginal cost (correct answer)
  3. The firm cannot be in long-run equilibrium because price exceeds minimum average cost, indicating short-run conditions
  4. The firm will produce 800 units to maximize the benefits from economies of scale before diseconomies begin
Explanation: With constant returns to scale between 500-800 units, the LRAC is flat at 10throughoutthisrange.Sinceprice(10 throughout this range. Since price (12) exceeds LRAC ($10), the firm earns economic profit and will produce where MR = MC within the 500-800 unit range. The exact output depends on the marginal cost curve. Choice A is wrong because any output in the 500-800 range minimizes LRAC, not just 650. Choice C is incorrect because firms can earn economic profits in long-run equilibrium if there are barriers to entry. Choice D is wrong because the firm should produce where MR = MC, not at the boundary of the constant returns range.

Question 6

A monopolistically competitive firm has a long-run average cost function where the minimum occurs at 400 units with a cost of $15 per unit. In long-run equilibrium, the firm produces 300 units and charges a price of $20. What can be concluded about this firm's situation?

  1. The firm has excess capacity of 100 units and economic profits of zero despite price exceeding minimum average cost (correct answer)
  2. The firm is operating inefficiently and should increase production to 400 units to minimize costs and maximize profits
  3. The firm has excess capacity but earns positive economic profits because barriers to entry prevent new firm entry
  4. The firm is in short-run equilibrium only, as long-run equilibrium requires production at minimum average cost
Explanation: In monopolistic competition's long-run equilibrium, firms produce where price equals average cost but not at minimum average cost due to product differentiation. The firm has excess capacity (400 - 300 = 100 units) but zero economic profit because P = AC at the chosen output level, even though this AC (20)exceedsminimumAC(20) exceeds minimum AC (15). Choice B ignores that the firm faces a downward-sloping demand curve. Choice C is wrong because monopolistic competition has free entry, driving economic profits to zero. Choice D misunderstands that long-run equilibrium in monopolistic competition doesn't require production at minimum AC.

Question 7

A firm in a perfectly competitive market is currently producing at an output level where its short-run average cost (SRAC) is on the upward-sloping portion of its U-shaped long-run average cost (LRAC) curve. The firm is making positive economic profit. Which of the following actions should the firm take to maximize its profit in the long run?

  1. Increase its plant size to take advantage of economies of scale.
  2. Decrease its plant size to mitigate the effects of diseconomies of scale. (correct answer)
  3. Maintain its current plant size as it is already earning positive economic profit.
  4. Exit the industry because it is operating inefficiently.
Explanation: The firm is operating on the upward-sloping portion of its LRAC curve, which indicates it is experiencing diseconomies of scale. This means its current plant size is too large for its current level of output to be produced at the lowest possible long-run average cost. Although it is currently profitable, in the long run, new firms will enter the market, driving the price down to the minimum of the LRAC. To survive and maximize long-run profit (which will be zero in competitive equilibrium), the firm must adjust its scale to be more efficient. It should decrease its plant size to move down and to the left along the LRAC curve toward the minimum efficient scale.

Question 8

A manufacturer of a complex product observes that its average cost per unit falls as its cumulative output increases over several years, despite its annual production rate and input prices remaining stable. This phenomenon is best described as:

  1. economies of scale.
  2. increasing marginal returns.
  3. learning by doing. (correct answer)
  4. a decrease in input prices.
Explanation: The scenario describes a situation where average costs fall with cumulative output, not the rate of output per period. This is the definition of learning by doing. As the firm and its workers gain experience over time, they become more efficient, reducing costs without any change in plant size or technology. Economies of scale (A) relate average cost to the scale of production within a given time period. Increasing marginal returns (B) is a short-run concept. The stem explicitly states that input prices remained stable, ruling out (D).

Question 9

A firm's long-run average cost (LRAC) curve is the lower envelope of its infinite number of short-run average cost (SRAC) curves. This structural relationship implies that for any given output level, the long-run total cost is:

  1. always greater than or equal to the short-run total cost.
  2. always less than or equal to the short-run total cost. (correct answer)
  3. equal to the short-run total cost only at the minimum efficient scale.
  4. unrelated to the short-run total cost as different inputs are variable.
Explanation: In the long run, a firm can adjust all of its inputs, including plant size, to minimize the cost of producing a given level of output. In the short run, at least one input is fixed. This extra constraint in the short run means that the cost of producing any output level (except for the one the plant was optimally designed for) will be higher than in the long run. Therefore, for any output Q, LRAC(Q)≤SRAC(Q)LRAC(Q) \le SRAC(Q), which implies that LRTC(Q)≤SRTC(Q)LRTC(Q) \le SRTC(Q). The costs are equal only at the output level for which the fixed input level of the SRAC curve is the long-run optimal choice.

Question 10

The rapid growth of an entire industry concentrated in a specific region leads to increased competition for skilled labor, driving up wages for all firms in that industry. This phenomenon results in which of the following for a representative firm?

  1. An upward shift of its long-run average cost curve. (correct answer)
  2. A movement to the right along its long-run average cost curve.
  3. A downward shift of its long-run average cost curve.
  4. A movement to the left along its long-run average cost curve.
Explanation: This scenario describes a pecuniary diseconomy of scale, an external effect where industry growth increases input prices for all firms. Since the cost of a key input (skilled labor) has risen, the cost of producing any given level of output is now higher. This causes the entire long-run average cost (LRAC) curve for a representative firm to shift upward. A movement along the LRAC curve would occur if the firm changed its own scale of production while input prices remained constant.

Question 11

All firms in a perfectly competitive industry have identical U-shaped long-run average cost (LRAC) curves. The minimum LRAC is $40, which occurs at an output of 500 units per firm. If the total quantity demanded in the market at a price of $40 is 1,000,000 units, what will be the number of firms in the industry in long-run equilibrium?

  1. 500
  2. 2,000 (correct answer)
  3. 2,500
  4. 25,000
Explanation: In long-run equilibrium for a perfectly competitive industry, two conditions must be met: 1) Price equals the minimum long-run average cost, and 2) Each firm produces at its minimum efficient scale (the output that minimizes LRAC). Here, the long-run price will be $40, and each firm will produce 500 units. To find the number of firms, divide the total market quantity demanded at that price by the quantity produced per firm: Number of firms = 1,000,000 units / 500 units/firm = 2,000 firms.

Question 12

Consider a specific level of output, q∗q^*, where a firm's short-run average cost (SRAC) curve for a given plant size is tangent to its long-run average cost (LRAC) curve. At this output level q∗q^*, which of the following statements must be true?

  1. The firm is operating at the minimum of both the SRAC and LRAC curves.
  2. The firm is experiencing constant returns to scale.
  3. Long-run marginal cost is equal to short-run marginal cost. (correct answer)
  4. Short-run marginal cost is at its minimum value.
Explanation: When you encounter questions about the tangency between short-run and long-run average cost curves, focus on what happens to marginal costs at the point of tangency. This tests your understanding of how firms optimize across different time horizons. At output level q∗q^* where SRAC is tangent to LRAC, both curves have the same slope. Since marginal cost represents the slope of the total cost curve, and average cost curves are derived from total cost curves, when average cost curves are tangent (same slope), their corresponding marginal costs must be equal. Therefore, short-run marginal cost equals long-run marginal cost at q∗q^*, making option C correct. Let's examine why the other options are incorrect. Option A assumes that tangency only occurs at the minimum points of both curves, but tangency can happen at any output level where the firm chooses the optimal plant size for that production level—not necessarily at either curve's minimum. Option B confuses the tangency condition with returns to scale. Constant returns to scale occur only when LRAC is horizontal (flat), which isn't required for tangency. The firm could be experiencing increasing or decreasing returns to scale at q∗q^*. Option D incorrectly suggests that short-run marginal cost must be at its minimum. The tangency condition tells us nothing about whether SRMC is at its minimum value—it could be rising, falling, or at its minimum. Remember this key insight: tangency between cost curves always implies equal marginal costs, regardless of whether you're at minimum points or experiencing particular returns to scale.

Question 13

A firm's long-run average cost curve exhibits economies of scale up to 1,000 units, then constant returns to scale from 1,000 to 2,000 units, then diseconomies of scale beyond 2,000 units. If the firm is currently producing 1,500 units and market conditions change such that optimal output becomes 2,500 units, what cost adjustment will the firm experience?

  1. Long-run average cost will increase gradually due to diminishing returns affecting all input combinations
  2. Long-run average cost will remain constant because the firm can adjust all inputs optimally in the long run
  3. Long-run average cost will decrease initially then increase as the firm transitions through different scale economies
  4. Long-run average cost will increase because the firm moves from constant returns to diseconomies of scale region (correct answer)
Explanation: When you encounter questions about long-run average cost curves, focus on how firms move between different regions of scale economies and the cost implications of those transitions. The firm is moving from 1,500 units (constant returns to scale region) to 2,500 units (diseconomies of scale region). In the constant returns region (1,000-2,000 units), long-run average cost remains flat - doubling all inputs doubles output while keeping per-unit costs unchanged. However, beyond 2,000 units, the firm enters diseconomies of scale, where long-run average cost rises as output increases due to coordination problems, management inefficiencies, and organizational complexities that emerge at very large scales. Since the firm moves from the constant returns region (where costs are stable) directly into the diseconomies region (where costs rise), the overall cost adjustment will be an increase in long-run average cost. Answer A incorrectly references diminishing returns, which applies to short-run production with fixed inputs, not long-run cost curves where all inputs are variable. Answer B wrongly assumes that optimal input adjustment prevents cost increases - while firms can adjust inputs optimally in the long run, this doesn't eliminate diseconomies of scale, which stem from fundamental organizational challenges at large scales. Answer C suggests the firm would experience decreasing costs initially, but since it's moving from constant returns (flat costs) to diseconomies (rising costs), there's no initial decrease. Remember: diseconomies of scale create unavoidable cost increases in the long run, regardless of optimal input combinations. Always identify which region of the cost curve the firm is moving between.

Question 14

If a firm is producing at an output level where its long-run average cost (LRAC) is decreasing, what must be true about the relationship between its long-run average cost and its long-run marginal cost (LRMC) at that output level?

  1. LRMC is greater than LRAC.
  2. LRMC must also be decreasing.
  3. LRMC is equal to LRAC.
  4. LRMC is less than LRAC. (correct answer)
Explanation: This question tests your understanding of the fundamental relationship between marginal and average costs. When you see questions about cost curves, always think about how marginal values drive changes in average values. When long-run average cost (LRAC) is decreasing, the firm is experiencing economies of scale. For any average to be falling, the marginal value must be pulling it down from below. Think of it like your GPA: if your cumulative GPA is falling, your current semester's GPA must be lower than your cumulative average. The same logic applies here. If LRAC is decreasing as output increases, then LRMC must be less than LRAC at that output level. The marginal cost of producing additional units is lower than the current average, which pulls the average down. Looking at the wrong answers: Choice A suggests LRMC is greater than LRAC, but this would cause LRAC to increase, not decrease. Choice B claims LRMC must also be decreasing, but this isn't necessarily true—LRMC could be increasing, constant, or decreasing as long as it remains below LRAC. Choice C states LRMC equals LRAC, which would mean LRAC is neither increasing nor decreasing, contradicting the given condition. The correct answer is D: LRMC is less than LRAC. Study tip: Remember the marginal-average relationship rule: when marginal is below average, average falls; when marginal is above average, average rises; when they're equal, average is at its minimum or maximum. This applies to all marginal-average relationships in economics, from costs to products.

Question 15

A firm faces a permanent increase in the government-mandated minimum wage, which affects all of its labor inputs. In the long run, the firm adjusts its production process to become more capital-intensive and less labor-intensive. How would these events be illustrated on a diagram of the firm's long-run average cost (LRAC) curve?

  1. A movement up and to the right along the initial LRAC curve.
  2. An upward shift of the entire LRAC curve. (correct answer)
  3. A downward shift of the entire LRAC curve.
  4. A movement down and to the left along the initial LRAC curve.
Explanation: An increase in the price of an input, like labor, makes it more expensive to produce any given level of output. This causes the firm's entire long-run average cost (LRAC) curve to shift upward. The firm's subsequent adjustment to use more capital and less labor is a cost-minimizing response to the higher wage rate. This adjustment determines the position of the new LRAC curve, but the overall effect of the input price increase is an upward shift of the cost curve. A movement along the curve would imply that input prices are constant.

Question 16

A firm's long-run production function is given by Q=K0.5L0.5Q = K^{0.5}L^{0.5}, where K is capital and L is labor. The rental rate of capital (r) is $25, and the wage rate (w) is $16. Which of the following represents the firm's long-run total cost (LRTC) as a function of output Q?

  1. LRTC=41QLRTC = 41Q
  2. LRTC=40QLRTC = 40Q (correct answer)
  3. LRTC=20Q2LRTC = 20Q^2
  4. LRTC=9QLRTC = 9\sqrt{Q}
Explanation: For long-run cost minimization, the firm sets the ratio of marginal products equal to the ratio of input prices: MPL/MPK=w/rMP_L/MP_K = w/r. Here, MPL=0.5K0.5L−0.5MP_L = 0.5K^{0.5}L^{-0.5} and MPK=0.5K−0.5L0.5MP_K = 0.5K^{-0.5}L^{0.5}. So, MPL/MPK=K/LMP_L/MP_K = K/L. Setting this equal to w/r=16/25w/r = 16/25 gives K/L=16/25K/L = 16/25, or K=(16/25)LK = (16/25)L. Substitute this into the production function: Q=((16/25)L)0.5L0.5=(4/5)L0.5L0.5=(4/5)LQ = ((16/25)L)^{0.5}L^{0.5} = (4/5)L^{0.5}L^{0.5} = (4/5)L. This implies L=(5/4)QL = (5/4)Q. From the K/L ratio, K=(16/25)L=(16/25)(5/4)Q=(4/5)QK = (16/25)L = (16/25)(5/4)Q = (4/5)Q. The total cost is LRTC=wL+rK=16L+25KLRTC = wL + rK = 16L + 25K. Substituting the expressions for L and K: LRTC=16((5/4)Q)+25((4/5)Q)=20Q+20Q=40QLRTC = 16((5/4)Q) + 25((4/5)Q) = 20Q + 20Q = 40Q.

Question 17

A firm uses two inputs, capital (K) and labor (L), to produce a good according to the production function Q=K0.4L0.7Q = K^{0.4}L^{0.7}. Assuming the prices of capital and labor are constant, what is the shape of this firm's long-run average cost (LRAC) curve?

  1. Downward sloping for all levels of output. (correct answer)
  2. Upward sloping for all levels of output.
  3. U-shaped.
  4. A horizontal line.
Explanation: The shape of the long-run average cost curve is determined by returns to scale. For a Cobb-Douglas production function of the form Q=KαLβQ = K^\alpha L^\beta, returns to scale are determined by the sum of the exponents α+β\alpha + \beta. In this case, the sum is 0.4+0.7=1.10.4 + 0.7 = 1.1. Since the sum is greater than 1, the firm experiences increasing returns to scale. Increasing returns to scale imply that as the firm increases all inputs by a certain proportion, output increases by a larger proportion. This leads to a long-run average cost that decreases as output expands. Therefore, the LRAC curve is downward sloping.

Question 18

A perfectly competitive industry is in long-run equilibrium. If demand increases permanently, what will happen to the number of firms and the long-run average cost of production for individual firms?

  1. Number of firms will increase; long-run average cost will remain unchanged for constant-cost industry conditions (correct answer)
  2. Number of firms will increase; long-run average cost will decrease due to improved production efficiency
  3. Number of firms will remain constant; long-run average cost will increase to accommodate higher demand
  4. Number of firms will increase; long-run average cost will increase due to resource competition effects
Explanation: In a constant-cost perfectly competitive industry, a permanent increase in demand leads to entry of new firms until the market returns to long-run equilibrium at the original price and minimum long-run average cost. Each firm produces at the same efficient scale as before. Choice B is wrong because LRAC doesn't change due to demand shifts in constant-cost industries. Choice C is incorrect because firms will enter rather than existing firms expanding beyond efficient scale. Choice D would only be correct in an increasing-cost industry where input prices rise with industry expansion.

Question 19

A multiproduct firm produces two goods, X and Y. Its long-run total cost function is LRTC(X,Y)=50X+60Y−0.1XYLRTC(X, Y) = 50X + 60Y - 0.1XY. This cost function implies that the firm's production process exhibits:

  1. economies of scope. (correct answer)
  2. diseconomies of scope.
  3. decreasing returns to scale.
  4. cost independence between the two products.
Explanation: Economies of scope exist when it is cheaper to produce two or more goods together in one firm than to produce them in separate firms. In a multiproduct cost function, this is indicated by a negative coefficient on the interaction term between the products. The term −0.1XY-0.1XY shows that as the production of one good increases, the marginal cost of producing the other good decreases. This complementarity in production leads to cost savings from joint production, which is the definition of economies of scope.

Question 20

If a single firm's long-run average cost curve is still declining when it is producing the entire quantity demanded in a market, the market is most likely a(n):

  1. perfectly competitive market.
  2. monopolistically competitive market.
  3. oligopoly.
  4. natural monopoly. (correct answer)
Explanation: A continuously declining long-run average cost (LRAC) curve over the relevant range of market demand signifies persistent economies of scale. This means that the largest firm will always have a cost advantage over smaller firms. Any potential competitor entering at a smaller scale would have higher average costs and would be unable to compete on price. Over time, the single largest firm will drive out all others, leading to a natural monopoly. The other market structures require that the minimum efficient scale be small relative to the total market demand.