Question

Distance covered by Ujjwal in 4 hours is 28 km against the stream and with stream 50 km in 2 hours. How much time Ujjwal will take to cover 32 km in still water ?
1. 2 hours
2. 2.5 hours
3. 1.5 hours
4. 3 hours
5. None of these.

Answer 1

Correct Answer - Option 1 : 2 hours

Given:

Distance covered in 4 hours in upstream = 28 km

Distance covered in 2 hours in downstream = 50 km

Formula used:

Speed of an object in downstream = x + y

Speed of an object in upstream = x – y

Speed of object in still water, x = (D + U)/2

Speed of stream, y = (D - U)/2

where,

D = Speed of object in downstream

U = Speed of object in upstream

Calculation:

Speed of object in upstream = 28/4

⇒ 7 km/h

Speed of object in downstream = 50/2

⇒ 25 km/h

Speed of object in still water, x = (D + U)/2

⇒ x = (7 + 25)/2

⇒ 16 km/h

Time taken to cover 32 km in still water

⇒ 32/16

⇒ 2 hours

∴ Ujjwal will take 2 hours to cover 32 km in still water.