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## Official Guide Explanation:Problem Solving #137

Background

This is just one of hundreds of free explanations I've created to the quantitative questions in The Official Guide for GMAT Quantitative Review (2nd 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: 137
Page: 79
Difficulty: 5 (Moderate)
Category 1: Word Problems > Mixture Problems >
Category 2: Arithmetic > Descriptive Statistics > Average

Explanation: This is a weighted average problem: Manfred received 6 \$750 paychecks and 20 \$780 paychecks. The typical weighted average formula would look like this:

((6(750) + 20(780))/26)

But because the actual numbers don't matter in a weighted average calculation, we can subtract 750 from each of the dollar amounts, so long as we remember to add 750 to the result when we're finished:

((6(0) + 20(30))/26) = ((0 + 600)/26) = (600/26) ≈ 23

Add 750 back to the average, for an answer of 750 + 23 = 773, choice (D).

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