ISEE Mathematics Achievement Question 320: Answer and Explanation

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Question: 320

4. There are 12 more girls than boys in a classroom. If there are 30 total students in the classroom, how many girls are there in the classroom?

  • A. 9
  • B. 12
  • C. 20
  • D. 21

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 how many girls are in the class, so label the choices "girls" and create another label next to it marked "boys." Test the choices, starting with (C). If there are 20 girls in the classroom, then subtract 12 to find the number of boys: 20 - 12 = 8 boys. 20 + 8 = 28, which means that (C) is too small. Eliminate (A), (B), and (C). Choice (D) must be the correct answer, so be aggressive if you're worried about the time. If you have time to check, you will see that it works because if there are 21 girls, then 21 - 12 = 9, so there are 9 boys. 21 + 9 = 30, which matches the total given in the problem. The correct answer is (D).

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