Official Guide Explanation:
Problem Solving #77




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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).

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