The speed of a stream is 3 mph. a boat travels 11 miles upstream in the same time it takes to travel 17 miles downstream. what is the speed of the boat in still water?

D=vt  (distance is equal to velocity times time)

let d=distance, b=velocity of boat, s=velocity of stream, and t=time

since d=vt, t=d/v

So for each trip we have:

t=11/(b-s) which is t=11/(b-3)

And for the downstream trip we have:

t=17/(b+s) which is t=17/(b+3)

Since we are told that each trip takes the same amount of time, t=t so we can say:

17/(b+3)=11/(b-3)  cross multiply we have:

17(b-3)=11(b+3)

17b-51=11b+33

6b=84

b=14

So the speed of the boat in still water is 14mph.