Kiara drove 120 miles from her home to a lake at an average... | SAT Ratios, rates, proportional relationships, and units Question, Answer Explained

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Math · Problem-Solving and Data AnalysisHard

Kiara drove $120$ miles from her home to a lake at an average speed of $40$ miles per hour. She returned home along the same route at an average speed of $60$ miles per hour. What was her average speed, in miles per hour, for the entire round trip?

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Answer: 48

The drive to the lake took $\frac{120}{40} = 3$ hours, and the drive home took $\frac{120}{60} = 2$ hours. The total distance is $240$ miles and the total time is $5$ hours, so the average speed is $\frac{240}{5} = 48$ miles per hour.

Averaging the two speeds gives $50$ , but Kiara spent more time driving at $40$ miles per hour, so her average speed is below $50$ .

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