Official Guide Explanation:
Problem Solving #3




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Solution and Metadata

Question: 3
Page: 62
Difficulty: 3 (Very Easy)
Category 1: Algebra > Equations >
Category 2: Word Problems > Other >

Explanation: If Mario was 32 years old 8 years ago, he's 40 now. x years ago, he was x years younger, so his current age is 40 - x. If you're not sure about how to apply that x, substitute a number for it: if you think about the arithmetic you do when you wonder, "how old was he 5 years ago," it may help clarify what to do with x.

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