Question

The speed of a stream is 3mph. 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?

Answer 1

Let x = speed of boat in still water
x-3 = speed up stream
x+3 = speed down stream
d=speed times time
11= (x-3) t
17=(x+3) t

t=11/(x-3)
t=17/(x+3) t=t
so 11/(x-3)=17/(x+3) cross multiply getting
11(x+3) = 17(x-3)
11x +33= 17x-51
16x=18
x=18/16=9/8 mph