Ritu can row downstream 20 km in 2 hours, and upstream 4 km in 2 hours. The speed of rowing in still water and the speed of the current is:

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6 km/h, 10 km/h

6 km/h, 4 km/h

3 km/h, 5 km/h

5 km/h, 10 km/h

answer is B.

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Detailed Solution

Given Ritu can row downstream 20 km in 2 hours, and she can row upstream 4 km in 2 hours.
Since,
Speed in upstream = speed in still water - speed of the stream
Speed in downstream = speed in still water + speed of the stream

Distance = speed × time

Let, Speed of rowing in still water = x
Speed of current = y
Downstream speed

=(x-y) kmph

Upstream speed

=(x+y) kmph

According to question,

2(x+y) = 20

x+y=10

----- 1
Also, for downstream,

2(x-y)=4

x-y = 2

---- 2
Adding equation 1 and 2,
(x + y) + (x – y) = 10 + 2
2x = 12
x = 6
The value of y is,
From equation 1,
6 + y = 10
y = 4
Still water speed = 6 km/h
Current speed = 4 km/h
Hence, option 2 is correct.

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