Official Guide Explanation:
Problem Solving #207




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Solution and Metadata

Question: 207
Page: 182
Difficulty: 6 (Moderately Difficult)
Category 1: Algebra > Linear Equations-One Unk >
Category 2: Word Problems > Rate Problems > other

Explanation: The variable isn't the usual one for a weighted average problem, but it still boils down to the same formula. The total number of days is n + 1, so the formula looks like this:

((50n + 90(1))/(n + 1)) = 55

50n + 90 = 55n + 55

35 = 5n

n = 7, choice (E).

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