ECON2011 Microeconomics Exam

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Questions and Answers

Matt views conditioner (C) and shampoo (S) as perfect complements, using one squirt of conditioner for each squirt of shampoo. If shampoo costs $1 per squirt and conditioner costs $2 per squirt, and Matt has $9 to spend, how many squirts of each will he buy?

Matt will buy 3 squirts of shampoo and 3 squirts of conditioner.

Geronimo's demand curve for apples is given by $a = \frac{p_bM}{p_a(p_a + p_b)}$, where $p_a$ is the price of apples, $p_b$ is the price of bananas, and $M$ is his income. Based on this information, are apples and bananas substitutes or complements? Explain.

Apples and bananas are substitutes. As the price of bananas ($p_b$) increases, the quantity of apples demanded (a) increases, indicating a substitution effect.

Andre's demand for doughnuts is given by $Q = 5 - p$, Baby's by $Q = 6 - 2p$, and Cooper's by $Q = 4 - \frac{p}{2}$. Derive the market demand for doughnuts, taking into account the maximum price each consumer will pay.

The market demand is Q = 15 - (7/2)p for $0 ≤ p ≤ 8$, Q = 11 - (5/2)p for $8 < p ≤ 10$, and Q = 5 - p for $10 < p ≤ 5.

Miquel and Jake's paper company uses the production function $Q = K^{1/2}L^{1/2}$ to produce reams of paper. They need to produce 10 reams of paper each week. If the price of capital (K) is $1 per unit and the price of labor (L) is also $1 per unit, how many units of each input should they use to minimize the cost of producing the 10 reams of paper? Explain.

<p>They should use 100 units of capital and 100 units of labor.</p> Signup and view all the answers

A firm's total cost is given by $C(Q) = 15Q^2 + 8Q + 45$, where Q is the quantity of output. Find the average cost (AC) as a function of quantity.

<p>The average cost function is $AC(Q) = 15Q + 8 + \frac{45}{Q}$.</p> Signup and view all the answers

A firm's total cost is given by $C(Q) = 15Q^2 + 8Q + 45$ where Q denotes the quantity of output. Find the marginal cost (MC) as a function of quantity.

<p>The marginal cost function is $MC(Q) = 30Q + 8$</p> Signup and view all the answers

A firm's total cost is $C(Q) = 15Q^2 + 8Q + 45$. For what quantities is the average cost greater than the marginal cost? Explain.

<p>The average cost is greater than the marginal cost for quantities Q &lt; 3/5 or Q &lt; 0.6.</p> Signup and view all the answers

A firm's total cost is given by $C(Q) = 15Q^2 + 8Q + 45$ where Q denotes the quantity of output. Find the average variable cost (AVC) as a function of quantity.

<p>The average variable cost function is $AVC(Q) = 15Q + 8$.</p> Signup and view all the answers

Cardboard boxes are produced in a competitive market. A firm in this market has the cost function $C(q) = 3q^3 - 18q^2 + 40q + 50$, where q denotes the quantity of output. Find the fixed cost and the variable cost functions.

<p>Fixed cost = 50 and Variable cost function is $VC(q) = 3q^3 - 18q^2 + 40q$.</p> Signup and view all the answers

A firm's cost function is $C(q) = 3q^3 - 18q^2 + 40q + 50$. Find the marginal cost function.

<p>The marginal cost function is $MC(q) = 9q^2 - 36q + 40$.</p> Signup and view all the answers

A firm's cost function is given by $C(q) = 3q^3 - 18q^2 + 40q + 50$. For what prices will the profit-maximizing output be greater than zero? Explain.

<p>The profit-maximizing output will be greater than zero for prices greater than the minimum value of the average variable cost ($AVC$). We can find $AVC$ by dividing the variable cost function ($VC$) by $q$. Hence, $AVC = 3q^2 - 18q + 40$. The derivative of this will give us: $6q - 18 = 0 \implies q = 3$. Plugging this into the $AVC$ yields $AVC = 13$.</p> Signup and view all the answers

Mariah consumes music downloads (x) and concert tickets (y). Her utility function is given by $U(x,y) = x^2 + 2y$. Find the equation for her indifference curve with $y$ as a function of $x$ when utility is equal to $U = 2$.

<p>The equation for the indifference curve is $y = 1 - \frac{x^2}{2}$.</p> Signup and view all the answers

Mariah consumes music downloads (x) and concert tickets (y). Her utility function is given by $U(x,y) = x^2 + 2y$. Using the indifference curve from part (a) of the original question, is the marginal rate of substitution (MRS) diminishing as x increases?

<p>The indifference curve is becoming steeper (MRS is not diminishing) as x increases.</p> Signup and view all the answers

Mariah consumes music downloads (x) and concert tickets (y). Her utility function is given by $U(x,y) = x^2 + 2y$. Do Mariah's preferences satisfy 'more is better'? Explain.

<p>Yes, but only for concert tickets. Holding the quantity of concert tickets (y) constant, more downloads (increasing x) increases utility if x is positive, but decreases utility if x is zero. So 'more is better' does not hold for downloads. Holding the quantity of downloads (x) constant, more concert tickets (increasing y) always increases utility regardless of x. So 'more is better' does hold for concert tickets.</p> Signup and view all the answers

Mariah consumes music downloads (x) and concert tickets (y). Her utility function is given by $U(x,y) = x^2 + 2y$. What consumption bundle(s) are optimal when each good costs $1 per unit and Mariah's total income is $10?

<p>The optimal consumption bundle is ⟨0, 10⟩.</p> Signup and view all the answers

Matt considers conditioner (C) and shampoo (S) as perfect complements and wants to consume one squirt of conditioner for each squirt of shampoo. Draw an indifference curve for (C, S) = (1,2). Be sure to label the axes and the point (1,2) on the indifference curve.

<p>The indifference curve is an L-shaped curve with the corner at (1,1).</p> Signup and view all the answers

Geronimo has the demand curve for apples given by $a = \frac{p_bM}{p_a(p_a + p_b)}$, where $p_a$ is the price of apples, $p_b$ is the price of bananas, and $M$ is Geronimo's income. Based on this information, is an apple a normal or inferior good? Explain why.

<p>Apples are a normal good. As income (M) increases, the quantity of apples demanded (a) increases, indicating a normal good.</p> Signup and view all the answers

Miquel and Jake run a paper company. Each week they need to produce 10 reams of paper. The production function for paper is given by $Q = K^{\frac{1}{2}}L^{\frac{1}{2}}$ where $Q$ is the number of reams of paper produced and $K$ and $L$ denote the number of inputs of capital and employed workers, respectively. Given these input prices, and the current production level $Q = 10$, what is the marginal cost of paper? Explain.

<p>The marginal cost of paper is approximately $0.1. This is because it costs 200 dollars to produce 10 reams of paper. We know this because capital and labor are each priced at $1 and 100 units of each are needed to produce 10 units of paper. $C(Q) = 2Q^2$, so $MC = 4Q = 400$. However, the function Q is not a continuous integer. To get from 10 to 11 Qs, $ \Delta{Q} = 1 $, $ \Delta{C(Q)} = 242 - 200 = 42$, so $MC = 42.</p> Signup and view all the answers

Miquel and Jake run a paper company. Each week they need to produce 10 reams of paper. The production function for paper is given by $Q = K^{\frac{1}{2}}L^{\frac{1}{2}}$ where $Q$ is the number of reams of paper produced and $K$ and $L$ denote the number of inputs of capital and employed workers, respectively. What is the average cost of paper at this level of production? Explain.

<p>The average cost of paper at this level of production is $20 dollars per ream of paper. Because the production function Q = 10 units of paper required 100 units of capital and 100 units of labor ($1 per unit), then the total cost of producing the 10 units is $200. The formula for average cost $AC = TC/Q$, so we have that the average cost $ = 200/10 = $20</p> Signup and view all the answers

Flashcards

Perfect Complements

Goods consumed together, like Matt's shampoo and conditioner, used in a fixed ratio.

Indifference Curve

A curve showing combinations of goods that give the consumer the same level of satisfaction.

Normal Good

A good for which demand increases as income increases.

Substitutes

Goods that can be used in place of each other.

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Market Demand

The total quantity demanded across all consumers in a market.

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Marginal Rate of Technical Substitution

The amount that one input must decrease to maintain the same level of production when another input increases.

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Marginal Cost

The cost to produce one more unit of output.

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Average Cost

Total cost divided by the quantity of output produced. (AC=TC/Q)

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Fixed Costs

Costs that do not vary with the level of output

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Variable Costs

Costs that change depending on the level of outputs

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Marginal Utility

Change in utility from consuming an additional unit of a good.

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Indifference Curve

A curve showing all combinations of which a consumer obtains the same utility, the consumer is indifferent.

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Marginal Rate of Substitution (MRS)

The rate at which a consumer is willing to trade one good for another while maintaining the same level of utility.

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Study Notes

  • This exam is for ECON2011 Principles of Microeconomics students at the St Lucia Campus.
  • The exam duration is 90 minutes, with a reading time of 10 minutes.
  • This is a School Examination and a Closed Book Examination.
  • Writing is only permitted on rough paper during reading time.
  • The examination paper will not be released to the Library.
  • No electronic aids are permitted (e.g., laptops, phones).
  • An unmarked Bilingual dictionary is permitted.
  • Calculators allowed are Casio FX82 series or UQ approved (labelled).
  • Students get a 1 x 14 Page Answer Booklet.
  • Answer all questions in your Answer Booklet(s).
  • Additional answer booklets and rough paper are provided upon request.
  • Total questions: 7
  • Total marks: 35

Question 1: Matt's Preferences for Conditioner and Shampoo

  • Matt views conditioner (C) and shampoo (S) as perfect complements and likes one squirt of conditioner for each shampoo squirt.
  • Part (a) requires drawing the indifference curve for (C, S) = (1,2), including labeled axes and the point (1,2).
  • Part (b) involves determining how many squirts of each Matt will buy with $9, given shampoo costs $1 per squirt and conditioner costs $2 per squirt.

Question 2: Geronimo's Demand for Apples

  • Geronimo’s demand curve for apples is given by 𝑎 = (𝑝𝑏𝑀) / (𝑝𝑎(𝑝𝑎 + 𝑝𝑏)), where pa > 0 and pb > 0 are the prices of apples and bananas, respectively, and M > 0 is Geronimo’s income.
  • Part (a) asks whether apples are a normal or inferior good based on the demand curve information.
  • Part (b) asks whether apples and bananas are substitutes or complements based on the demand curve information.

Question 3: Market Demand for Doughnuts

  • Andre’s demand for doughnuts is given by Q = 5 – p, Baby’s by Q = 6 – 2p, and Cooper’s by Q = 4 - p/2.
  • Part (a) requires deriving the market demand for doughnuts, considering the maximum price each consumer will pay.
  • Part (b) requires drawing the market demand curve.

Question 4: Miquel and Jake's Paper Company

  • Miquel and Jake need to produce 10 reams of paper weekly with the production function Q = K^(1/4) * L^(1/4), where Q is reams of paper, K is capital, and L is labor.
  • The price of K is $1 per unit, and the price of L is also $1 per unit.
  • Part (a) asks for the units of each input that minimize the cost of producing 10 reams of paper.
  • Part (b) asks for the marginal cost of paper, given the input prices and a production level of Q = 10.
  • Part (c) asks for the average cost of paper at the same production level.

Question 5: Firm's Total Cost and Output

  • A firm's total cost is given by C(Q) = 15Q² + 8Q + 45, where Q is the quantity of output.
  • Part (a) asks to find the average cost as a function of quantity.
  • Part (b) asks to find the marginal cost as a function of quantity.
  • Part (c) asks at what quantities the average cost is greater than the marginal cost.
  • Part (d) asks to find the average variable cost as a function of quantity.

Question 6: Cardboard Boxes in a Competitive Market

  • A firm in a competitive market produces cardboard boxes with a cost function C(q) = 3q³ – 18q² + 40q + 50, where q is the quantity of output.
  • Part (a) asks to find fixed cost and variable cost functions.
  • Part (b) asks to find the marginal cost function.
  • Part (c) asks at what prices the profit-maximizing output will be greater than zero.

Question 7: Mariah's Consumption of Music Downloads and Concert Tickets

  • Mariah's utility function for music downloads (x) and concert tickets (y) is U(x,y) = x² + 2y.
  • Part (a) asks for the equation for Mariah's indifference curve with y as a function of x when utility U = 2.
  • Part (b) asks to use the indifference curve from part (a) to determine if the indifference curve is becoming flatter (diminishing MRS) as x increases.
  • Part (c) asks, do Mariah’s preferences satisfy more is better?
  • Part (d) asks what consumption bundles are optimal when each good costs $1 per unit, and Mariah's total income is $10.

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