At the local F1 race track, Alex was testing the latest car.

During the eight test laps, Alex managed to average the first two laps at 100mph, the next two laps at 102mph, the next two laps at 140mph, and the last two laps at 150mph.

What was the average speed for the entire 8 laps?

Puzzle Copyright © Kevin Stone

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Hint

It doesn't matter how long a lap is.

Answer

119mph.

Set the track length to be a random number, e.g. 5 miles.

Therefore the first two laps took 10 miles ÷ 100 mph = 10 ÷ 100 hours. Similarly, the second two laps took 10 ÷ 102 hours, etc. The total time taken for 40 miles is, therefore, 10/100 + 10/102 + 10/140 + 10/150 hours.

Therefore the average speed for the entire 8 laps is 40 ÷ (10÷100 + 10÷102 + 10÷140 + 10÷150) = 119 mph.