A boy swims downstream 0.9 miles in the same amount of time that he can swim 0.6 miles upstream. If the rate of the current is 1.5 mph, how fast can he swim in

Question

A boy swims downstream 0.9 miles in the same amount of time that he can swim 0.6 miles upstream. If the rate of the current is 1.5 mph, how fast can he swim in still water?

A. 0.2 mph

B. 0.75 mph

C. 7.5 mph

Answer 1

I think the problem is misstated. It should be 9 mi and 6 mi instead of .9 and .6 as these will give negative velocity. Let v be the speed he can swim in still water and t the time for both up and down stream. The current is 1.5. Then the distances he swims are (v+1.5)*t = 9, (v-1.5)*t=6. Equatining the value for t (up = down) gives  9/(v+1.5) = 6/(v-1.5) or

3v = 22.5, v=7.5 or C above. Actually since there are two equations in one unknown one could set t=1 and solve either equation.