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.