A motor-boat can travel upstream at a speed of 10 miles per hour and downstream at a speed of 14 miles per hour. If the boat travels at a constant speed, what is the speed at which the stream is flowing?
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1 mile per hour
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2 miles per hour
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3 miles per hour
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4 miles hour
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None Of These
B
Correct answer
Explanation
Let boat speed in still water = b, stream speed = s. Upstream: b - s = 10. Downstream: b + s = 14. Adding: 2b = 24, so b = 12 mph. Then s = 14 - 12 = 2 mph. The stream flows at 2 mph. This is a classic boats and streams problem - the key is recognizing that downstream speed is sum and upstream is difference.