Chris’ Average Expenses

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Chris' average (arithmetic mean) daily expenses were $500 per day over a 15-day trip. During this period, if Chris' average daily expenses were $450 for the first 5 days, what were the average daily expenses for the last 10 days?

Review: Chris' Average Expenses


Explanation

We can solve this question quickly with the knowledge that differences from the average in a group of numbers must net to zero. If the trip were 10 days, and the first 5 days were $450, then the last 5 days would average $550 for the overall balance to be $500. But there are twice as many days in the second group, so it carries twice as much weight. Therefore, it must be half as far from $500 to $550, or $525.

The correct answer is (C).


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