Question

A girl is swimming downstream. In still water she can swim at 2km/h and the river is flowing with her. She covered a distance of 12km in 2h 24 min. How fast was the stream flowing?

Answer 1

The speed of stream is 3 km/hr

Solution:

Given that girl is swimming downstream

To find: Speed of stream

In still water she can swim at 2km/h and the river is flowing with her

Speed in still water = 2 km/hr

She covered a distance of 12km in 2h 24 min

Distance = 12 km

time taken = 2h 24 min =
`2 + (24)/(60) = 2.4 hours`

Therefore,

`speed = (distance)/(time)`

`speed downstream = (12)/(2.4) = 5 \text{ kilometer per hour }`

If the speed of a boat in still water is u km/hr and the speed of the stream is v km/hr, then:

Speed downstream = (u + v) km/hr

5 km/hr = 2 km/hr + v

v = 5 - 2

v = 3 km\hr

Thus speed of stream is 3 km/hr