Andrew M. answered • 09/12/17
Tutor
New to Wyzant
Mathematics - Algebra a Specialty / F.I.T. Grad - B.S. w/Honors
the speed of a stream is 3 mph. a boat travels 4 miles upstream
in the same time it takes to travel 10 miles downstream
Upstream: speed = boat speed - current speed = b-c = b-3
Downstream: speed = boat speed + current speed = b+c = b+3
distance = rate*time ... d=rt
rearranging: t = d/r
Upstream: t = 4/(b-3)
Downstream: t = 10/(b+3)
4/(b-3) = 10/(b+3)
4(b+3) = 10(b-3)
4b+12 = 10b-30
6b = 42
b = 7mph speed for boat in still water
