ISEE Mathematics Achievement Question 322: Answer and Explanation

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Question: 322

6. Adam is half as old as Bob and three times as old as Cindy. If the sum of their ages is 40, what is Bob's age?

  • A. 6
  • B. 12
  • C. 18
  • D. 24

Correct Answer: D

Explanation:

D The question is asking for a specific value and there are real numbers in the choices, so use PITA to solve. The question asks for Bob's age, so label the choices "Bob" and create 2 additional columns next to it, one labeled as Adam and the other as Cindy. Now, follow the steps of the question and test the choices, starting with (C). If Bob is 18, then Adam must be 9 because Adam is half as old as Bob. It is also stated that [Adam] is three times as old as Cindy (remember, Adam is the subject of the sentence), so Cindy must be 3 since = 3. Find the total of their ages: 18 + 9 + 3 = 30, which is too small. Eliminate (A), (B), and (C). Choice (D) is the only answer left, so it must be correct. Stop work and move on! If you have time later to check, you'll see that if Bob is 24, then Adam must be 12 and Cindy is 4, which makes the total 24 + 12 + 4 = 40. The correct answer is (D).

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