Official Guide Explanation:
Problem Solving #91




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Solution and Metadata

Question: 91
Page: 165
Difficulty: 4 (Moderately Easy)
Category 1: Algebra > Linear Equations-Two Unk >

Explanation: If the price of a map is m and the price of a book is b , we can set up two equations:

12m + 10b = 38

20m + 15b = 60

We're looking for b - m, the difference in the prices of each type of product.

The easiest way to combine the two equations is to start by multiplying the first by (3/2), so that both equations contain a 15b:

18m + 15b = 57

We can now subtract this equation from the second:

2m = 3

m = 1.5

Substitute m into the second equation to find b:

20(1.5) + 15b = 60

30 + 15b = 60

15b = 30

b = 2

The difference, then, is 2 - 1.5 = 0.5, choice (B).

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