Question

A motorboat maintained a constant speed of 10 miles per hour relative to the water in going 19 miles upstream and then returning. The total time for the trip was 20.0 hours. Use this information to find the speed of the current.

Answer 1

Let c be the speed of the current. Then:
19/10+c + 19/10-c=20
19(10+c)+19(10-c)=2000-20c²
20c²-1620=0
20c²=1620
c²=81
c=+/-9
The speed of the current was 9 mph. ☺☺☺☺