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## Official Guide Explanation:Problem Solving #175

Background

This is just one of hundreds of free explanations I've created to the quantitative questions in The Official Guide for GMAT Review (12th ed.). Click the links on the question number, difficulty level, and categories to find explanations for other problems.

These are the same explanations that are featured in my "Guides to the Official Guide" PDF booklets. However, because of the limitations of HTML and cross-browser compatibility, some mathematical concepts, such as fractions and roots, do not display as clearly online.

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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