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MCQ Practice Single Best Answer Topic: Time and Distance

Q In calm water, a man may swim at a speed of 10 kilometres per hour. When he swims up the river, it takes him twice as long as when he swims down the river to reach his target. How fast is the river flowing?

Question ID
#4718
Subchapter
Time and Distance
Action
Choose one option below

Choose Your Answer

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  • A 10?3 km/hr ✔ ✖
  • B 8?2km/hr ✔ ✖
  • C 11?7km/hr ✔ ✖
  • D 10?5 km/hr ✔ ✖
Correct Answer: A

Explanation


The speed of the river is X km/hr, and the man has a downward speed of 10 + X km/hr when he swims with the flow of the river, and an upward speed of 10 - X km/hr when he swims against the flow.

The problem states that the time it takes the man to cover a distance Y when he swims up the river is double the time it takes him to cover the same distance when he swims down the river.

To solve for the speed of the river, we can set up the following equation: Y/(10-X) = 2 * Y/(10+X)

We can then solve for X as follows:

10Y + XY = 20Y - 2XY
XY + 2XY = 20Y - 10Y
3XY = 10Y
3X = 10
X = 10/3 = <<10/3=3.333>>3.333 km/hr

Therefore, the speed of the river is approximately 3.333 km/hr.

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