Question

A boat which moves a 15 miles per hour without a current goes 36 miles upstream and 36 miles back in 5 hours. Find the speed of the current

Answer 1

3 mph

Explanation:

UPSTREAM:

distance = 36 miles ;

Speed = 15-c mph ;

TIME, t = distance / speed = 36/(15-c)

Downstream :

distance = 36 miles ;

speed = 15+c mph ;

time, t = 36/(15+c)

upstream time + downstream time = 5 hrs

36/(15-c) + 36/(15+c) = 5

36(15+c) + 36(15-c) = 5(15-c)(15+c)

1080 = 5(225 - c²)

1080 / 5 = 225 - c²

216 = 225 - c^2

216 - 225 = c²

-9 = c²

c = 3