Question
A boy can swim a certain distance downstream in 3 hours
and return in 7 hours. If the rate of stream is 4 kmph then what is the speed of boy in still water?Solution
Let the speed of the boy in still water be x kmph. Then, (x + 4) × 3 = (x – 4) × 7 => 3x + 12 = 7x - 28 => 4x = 40 => x = 10 kmph
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