at full throttle

Question

At full throttle, the boat went upstream 32 miles in 8 times the time it took to go downstream 32 miles at full throttle.  If the current was 7 miles per hour, what is the speed of the boat in still water?

Answer 1

Let S = speed in still water

Upstream speed = S-7 and downstream speed = S+7

8(S-7) = S+7

 

8S - 56 = S + 7

Subtract S from each side and add 56 to each side => 7S = 63 and S = 9