The speed of a boat in still water is 9 km/hr and the speed of the stream is 6 km/hr. The boat goes a distance of 90 km upstream and comes back to the starting point. What is the total time (in hours) taken by the boat?
Show answer & explanation
Correct answer: A
Explanation
Given:
Speed in still water = 9 km/h
Speed of the current = 6 km/h
Distance = 90 km
According to the formula:
Speed upstream = 9 − 6
Speed downstream = 9 + 6
Time = Distance / Speed
Upstream speed = 3 km/h
Downstream speed = 15 km/h
Upstream time = 90 / 3 = 30 hours
Downstream time = 90 / 15 = 6 hours
Total time = 30 + 6 = 36 hours