A motorboat can maintain a constant speed of 12 miles per hour relative to the water. The boat makes a trip upstream in 42 minutes and the return trip takes 21 minutes. What is the speed of the current?
A) 0.3 mph
B) 12 mph
C) 4.0 mph
D) 24 mph

Question

Quizplus · Accepted Answer

The speed of the boat relative to the water is 12 mph. Let the speed of the current be x mph. Upstream, the effective speed is (12 - x) mph, and downstream, it is (12 + x) mph. The time taken upstream is 42 minutes (0.7 hours) and downstream is 21 minutes (0.35 hours). Using the formula distance = speed × time, the distances for both trips are equal: (12 - x) * 0.7 = (12 + x) * 0.35. Solving this equation gives x = 4 mph.

A Motorboat Can Maintain a Constant Speed of 12 Miles