Consumer Choice Practice Questions

8 representative multiple-choice questions on consumer choice for AP Microeconomics, drawn from our 15-question bank for this module. Work through each one, then open “Show answer” for the correct choice and an explanation. For scored, timed practice across the full bank, take a full practice test.

1. 1. A consumer is maximizing utility when which of the following conditions is met?

   • A. Total utility is equal for all goods consumed
   • B. Marginal utility is equal for all goods consumed
   • C. Marginal utility per dollar spent is equal for all goods consumed
   • D. The consumer spends equal amounts on each good
   Show answer

   Correct answer: C. Marginal utility per dollar spent is equal for all goods consumed

   The utility-maximizing rule is MU/P equal across all goods, not raw MU, not total utility, and definitely not equal dollar amounts. B ignores prices entirely, which is a problem because a good with sky-high marginal utility but a massive price tag might deliver terrible value per dollar. A confuses total with marginal utility, and total utility levels across different goods have nothing to do with the optimization condition.

2. 2. The law of diminishing marginal utility helps explain which of the following?

   • A. Why supply curves slope upward
   • B. Why demand curves slope downward
   • C. Why firms earn zero economic profit in the long run
   • D. Why governments impose price floors
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   Correct answer: B. Why demand curves slope downward

   Each additional unit gives you less satisfaction, so you'll only buy the next unit if the price drops enough to justify that lower marginal utility. That's a downward-sloping demand curve. A is about increasing marginal costs on the production side, which is a completely different concept on a different side of the market. C is about firm entry and exit in competitive markets, which has nothing to do with how individual consumers value successive units of a good.

3. 3. A consumer currently buys goods X and Y. The marginal utility of X is 30 and its price is $5. The marginal utility of Y is 20 and its price is $10. To maximize utility, the consumer should:

   • A. Buy more of both X and Y
   • B. Buy more of X and less of Y
   • C. Buy more of Y and less of X
   • D. Make no changes; utility is already maximized
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   Correct answer: B. Buy more of X and less of Y

   Do the math. MU_X / P_X = 30/5 = 6 utils per dollar. MU_Y / P_Y = 20/10 = 2 utils per dollar. X gives triple the satisfaction per dollar, so shift spending from Y toward X. As you buy more X, diminishing marginal utility drags MU_X down; as you buy less Y, MU_Y rises. Eventually the ratios converge and you're at equilibrium. D is wrong because 6 doesn't equal 2 and the current allocation is clearly leaving satisfaction on the table.

4. 4. Which of the following best describes the substitution effect of a price decrease?

   • A. The consumer feels wealthier and buys more of all goods
   • B. The consumer buys more of the good because it is now relatively cheaper than alternatives
   • C. The consumer's demand curve shifts to the right
   • D. The consumer reaches a higher budget constraint through increased income
   Show answer

   Correct answer: B. The consumer buys more of the good because it is now relatively cheaper than alternatives

   The substitution effect isolates the price-ratio change while holding real income constant. Good A got cheaper relative to Good B, so you substitute toward A. That's it. A describes the income effect. The feeling-wealthier part is about purchasing power, not relative prices. C is wrong because a change in a good's own price causes movement along the demand curve, not a shift of the whole curve.

5. 5. If the price of an inferior good decreases, the income effect will cause the consumer to:

   • A. Buy more of the inferior good
   • B. Buy less of the inferior good
   • C. Buy the same amount of the inferior good
   • D. Switch entirely to a substitute good
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   Correct answer: B. Buy less of the inferior good

   The price drop raises real income. By definition, when income goes up consumers buy less of inferior goods, so the income effect alone pushes quantity down. The substitution effect still pushes quantity up (the good is relatively cheaper). For most inferior goods the substitution effect wins overall and quantity still increases on net. But the question asks specifically about the income effect in isolation, and that component reduces purchases. A describes the income effect for a normal good, not an inferior one.

6. 6. A consumer eats four slices of pizza and reports the following total utilities: 1st slice = 20 utils, 2nd slice = 36 utils, 3rd slice = 46 utils, 4th slice = 50 utils. The marginal utility of the 3rd slice is:

   • A. 46 utils
   • B. 15.3 utils
   • C. 10 utils
   • D. 4 utils
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   Correct answer: C. 10 utils

   Marginal utility = change in total utility from one more unit. For the 3rd slice: 46 - 36 = 10 utils. A (46) is the total utility after three slices, not the marginal gain from the third one. B (15.3) comes from dividing total utility by quantity (46/3), which gives you average utility, a different concept entirely. D (4 utils) is the marginal utility of the 4th slice (50 - 46), not the 3rd.

7. 7. A consumer's income doubles while all prices remain constant. The budget constraint will:

   • A. Rotate outward along one axis only
   • B. Shift outward in a parallel fashion, doubling the intercepts on both axes
   • C. Become steeper because the consumer can now afford more expensive goods
   • D. Remain unchanged because relative prices have not changed
   Show answer

   Correct answer: B. Shift outward in a parallel fashion, doubling the intercepts on both axes

   Double the income with prices unchanged and both axis intercepts double. The slope equals the negative ratio of prices, and since neither price changed, the slope stays the same. Parallel outward shift. A describes what happens when one price changes (rotation). D makes the mistake of confusing relative prices with purchasing power. Relative prices didn't change, true, but the set of affordable bundles clearly expanded when income doubled.

8. 8. A consumer values the 100th gallon of water at $0.01 and a 1-carat diamond at $5,000. Water is essential for survival and diamonds are not, yet diamonds cost far more. This paradox is best explained by:

   • A. Diamonds are more useful than water in total
   • B. The marginal utility of water is very low because water is abundant, while the marginal utility of diamonds is high because they are scarce
   • C. Consumers are irrational in their purchasing decisions
   • D. The supply of diamonds is perfectly elastic
   Show answer

   Correct answer: B. The marginal utility of water is very low because water is abundant, while the marginal utility of diamonds is high because they are scarce

   The diamond-water paradox disappears once you separate marginal utility from total utility. Water's total utility is immense because you literally die without it. But at typical consumption levels water is so abundant that the next gallon adds almost nothing. Diamonds are scarce, so each additional one carries high marginal utility. Market prices reflect marginal utility, not total. Adam Smith posed this puzzle in 1776; the marginalist economists of the 1870s (Jevons, Menger, Walras) finally resolved it. A is factually wrong. Water's total utility dwarfs diamonds'. C is a non-answer that explains nothing.