A motorboat maintained a constant speed of 30 miles per hour relative to the water in going 20 miles upstream and then returning. The total time for the trip was 1.5 hours. Use this information to find the speed of the current.
Let the speed of the current ==w
20 / (30 - w) + 20 / (30 + w)==1.5, solve for w
w == 10 mph - the speed of the current.