If a boat goes 7 km upstream in 42 minutes and the speed of the stream is 3 kmph, then the speed of the boat in still water is:

12 kmph

13 kmph

14 kmph

15 kmph

Rate upstream = (7/42)*60 kmh = 10 kmph. Speed of stream = 3 kmph. Let speed in sttil water is x km/hr Then, speed upstream = (x - 3) km/hr. => x-3 = 10 or x = 13 kmph

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