Question

A motorboat, that has speed of 10 km/hour in still water, left a pier traveling against the current of the river. Forty-five minutes after the boat left the pier, the motor of the boat broke, and the boat began drifting with the current. After three hours of drifting with the current, the boat was back at the pier where it had started. What is the speed of the current of the river?

Answer 1

Answer:

2 km/h

Step-by-step explanation:

• distance = speed × time
• time = distance/speed

Let c represent the speed of the current of the river in km/h. Then the speed of the boat upstream is (10-c). In 3/4 hour, the distance traveled upstream is ...

... distance upstream = (3/4)·(10 -c)

The time taken to travel the same distance downstream is given as 3 hours. The speed in that direction is c, so we have ...

... 3 = distance upstream/c = (3/4)(10 -c)/c

Multiplying this equation by 4c, we get ...

... 12c = 3(10 -c)

... 15c = 30 . . . . . . . . add 3c

... c = 2 . . . . . . . . . . . divide by 15

The speed of the river current is 2 km/h.