Official Guide Explanation:
Problem Solving #220




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Solution and Metadata

Question: 220
Page: 184
Difficulty: 6 (Moderately Difficult)
Category 1: Arithmetic > Percents > Percent Change
Category 2: Word Problems > Rate Problems > other

Explanation: This is a question where assigning numbers to unknown values comes in handy. Say the employee's original number of hours per week was 10, and the original pay rate was $8 per hour. That's $8(10) = $80 per week. If the pay rate increases by 25%, that's an increase of 25%($8) = $2 to $8 + $2 = $10 per hour. To make $80 per week at an hourly rate of $10 per hour, the employee needs to work (($80)/($10)) = 8. Percent change is ((change)/(original)), so in this case, when the hours decreased from 10 to 8, that's ((10 - 8)/10) = (2/10) = 20%, choice (B).

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