Chen's motorgoat took 3 hr to make a treip downstream with a 6-mph current. The return trip against the same current took 5 hr. Find the speed of the boat in still water.

Answer 1

since distance=speed*time, if the boat's speed is x, we have

3(x+6) = 5(x-6)

Answer 2

eq 1: y miles/(6 mph + x mph)=3 hr
eq 2: y miles/(6 mph - x mph)=5 r

multiply both sides by the numerator on the left

eq 1: y =18 + 3x
eq 2: y =30 - 5x

subtract equation 2 from equation 1

0=-12 + 8x
12=8x
12/8+x