It took a crew 4 hr 16 min to row 4 km upstream and back again. If the rate of flow of the stream was 7 km/h, what was the rowing speed of the crew in still water?

Answer 1

I am not going to solve this for you, but I will tell you how to do it.

Let S be the rowing speed in still water, T_w be the time rowing with the current and T_a be the speed rowing against the current.

4 miles is the distance rowed in each direction.

(S+7)T_w = 4 and (S-7)T_a = 4

T_w = 4/(S+7) and T_a = 4/(S-7)

Add the 2 equations and remember that T_w + T_a = 4 4/15 hours

[1/(S+7)] + [1/(S-7)] = 1 1/15

2S/(S²-49) = 1 1/15

Multiply this out and collect terms to get a quadratic equation is S.