Question

Amotorboat can maintain a constant speed of 10 miles per hour relative to the waterThe boat makes a trip upstream to a certain point in 54 minutes the return trip takes 18 minutes. What is the speed of the current

Answer 1

20 mph.

Explanation:

Let the speed of the current be x mph.

54 minutes = 54/60 = 0.9 hours and 18 minutes = 18/60 = 0.30 hours

Travelling against the current:

Speed = distance / time

x - 10 = d / 0.9

With the current:

x + 10 = d / 0.3

Subtract the second equation from the first:

0 - 20 = d/0.9 - d/0.3

-20 = (d - 3d) / 0.9

-20 * 0.9 = -2d

-2d = -18

d = 9

So x + 10 = 9/0.3 = 90/3

x + 10 = 30

x = 20 mph.