2008 AMC 8 Problem 20

Below is the professionally curated solution for Problem 20 of the 2008 AMC 8, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2008 AMC 8 solutions, or check the answer key.

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Concepts:least common multipleratio and proportion

Difficulty rating: 1380

20.

The students in Mr. Neatkin's class took a penmanship test. Two-thirds of the boys and 34\frac{3}{4} of the girls passed the test, and an equal number of boys and girls passed the test. What is the minimum possible number of students in the class?

 12 \ 12

 17 \ 17

 24 \ 24

 27 \ 27

 36 \ 36

Solution:

Let pp be the common number of boys and girls who passed.

Since 23\dfrac{2}{3} of the boys passed, the number of boys is 3p2\dfrac{3p}{2}. Since 34\dfrac{3}{4} of the girls passed, the number of girls is 4p3\dfrac{4p}{3}.

The smallest positive pp that makes both counts whole is 66. Then there are 99 boys and 88 girls, for a minimum total of 1717 students.

Thus, B is the correct answer.

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