A boat travels 30 km upstream and 44 km downstream in a total of 10 hours. If the stream flows at 3 km/h, the speed of the boat in still water is:

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Accepted Answer

8 km/h. With still-water speed x, 30/(x − 3) + 44/(x + 3) = 10. Clearing denominators gives 74x − 42 = 10x² − 90, i.e. 5x² − 37x − 24 = 0, whose positive root is x = 8 (since 5 × 64 − 37 × 8 − 24 = 0). Check: 30/5 + 44/11 = 6 + 4 = 10 hours.

A boat travels 30 km upstream and 44 km downstream in a total of 10 hours. If the stream flows at 3 km/h, the speed of the boat in still water is:

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