Average speed over three laps

EasyBrainteasers~3m

A car laps a track three times: the first lap at $100$ mph, the second at $150$ mph, and the third at $200$ mph (each lap the same distance). What is the car's average speed over all three laps (mph)?

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Average speed $=$ total distance $/$ total time; use equal distances per lap.
It's the harmonic mean: $3/(\tfrac1{100}+\tfrac1{150}+\tfrac1{200})=\tfrac{1800}{13}$ .

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138.46 (± 0.05)

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Average speed over three laps

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