Official Guide Explanation:
Problem Solving #175




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Solution and Metadata

Question: 175
Page: 177
Difficulty: 5 (Moderate)
Category 1: Arithmetic > Fractions >
Category 2: Word Problems > Rate Problems > other

Explanation: To find the total number of students in the course, we need to know the fraction of students who got D's. With that fraction, we can covert the number of D's (10) into the total number of students. The fraction of non - D's is given by the sum of the A's, B's, and C's: (1/5) + (1/4) + (1/2) = (4/20) + (5/20) + (10/20) = (19/20). That leaves 1 - (19/20) = (1/20) of the total as D's. If 10 is (1/20) of the total, that means that the total is 10(20) = 200, choice (D).

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