Math CentralQuandaries & Queries


Question from tien:

a boat travels upstream, against a current, at a speed of 4 miles per hour. On the return trip, the boat travels downstream, with the current , at 10 miles per hour. the speed of the current remains constant. what is the speed of the current?


Suppose the speed of the boat in still water is b miles per hour and the speed of the current is c miles per hour. Travelling upstream, against the current, the speed of the boat is then b - c miles per hour. Thus

b - c = 4 miles per hour.

What is the speed of the boat downstream, with the current? You know this is 10 miles per hour. This gives you a second equation in b and c. Solve for c.


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