Question

Ravish can swim in still water at the rate of 15 km/h. He takes half as long to swim downstream than upstream then find the speed of stream (in km/h).
1. 8
2. 5
3. 7
4. 4
5. 10

Answer 1

Correct Answer - Option 2 : 5

Given

Speed of Ravish in still water = 15 km/h

Formula used

Downstream speed = Speed in still water + Speed of steam

Upstream speed = Speed in still water – Speed of steam

Calculation

Let the speed of stream = x km/h

Then speed of downstream = (15 + x) km/h

Speed of upstream = (15 - x) km/h

As the time taken downstream is half that of the time taken upstream,

Downstream speed = 2 × (upstream speed)

15 + x = 2 (15 - x)

⇒ 15 + x = 30 - 2x

⇒ 3x = 15

⇒ x = 5 km/h

∴ The speed of steam is 5 Km/h