Official Guide Explanation:
Problem Solving #27




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Solution and Metadata

Question: 27
Page: 156
Difficulty: 5 (Moderate)
Category 1: Arithmetic > Descriptive Statistics > Average

Explanation: If the student has an average score of 78 on four tests, the total score is 4(78). If the average on five tests is to be 80, that's a total of 5(80). If we call the fifth test score x, we can set up an equation representing the total of the five scores in two different ways:

4(78) + x = 5(80)

312 + x = 400

x = 88, choice (E).

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