Official Guide Explanation:
Problem Solving #77

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.

Click here for an example of the PDF booklets. Click here to purchase a PDF copy.

Solution and Metadata

Question: 77
Page: 71
Difficulty: 5 (Moderate)
Category 1: Word Problems > Measurement Problems >
Category 2: Algebra > Linear Equations-Two Unk >

Explanation: It may not be obvious amidst all the definitions, but this problem is straightforward algebra: it gives you two equations with two variables. Since the variables are equal, you can combine the equations and solve for either variable. Since the second equation, F = C, already has each variable in terms of the other, we can substitute directly into the first equation:

C = (9/5)C + 32

C - (9/5)C = 32

(5/5)C - (9/5)C = 32

-(4/5)C = 32

C = 32(-(5/4))= - (8)(5)= - 40, choice (E).

Click here for the full list of GMAT Quant Review explanations.

Total GMAT Math The comprehensive guide to the GMAT Quant section. It's "far and away the best study material available," including over 300 realistic practice questions and more than 500 exercises! Click to read more.