Question

A motor-boat can travel at 10 km/hour in still water. It travelled 91 km downstream in a river and then returned to the same place, taking altogether 20 hours. Find the rate of flow of river

• A. 3 km/hour
• B. 4 km/hour
• C. 2 km/hour
• D. 5 km/hour

Answer 1

Answer:

A. 3 km/hour

Let the flow of the river be x km/h. Then, speed downstream = ( X + 10)km/h speed upstream = ( 10 - X) km/hr 91/((X + 10) + 91/( 10 - X) = 20 91[20/((10 + X)(10 - X)] = 20 (10 + X)(10 - X) = 91 100 - X² = 91 X² = 9 X = 3 The rate of flow of river 3Km/hr