Question

The Dolphin in river can swim with a speed of 15 km/h in still water. If the speed of the stream is 4 km/h, find the time taken (in hours) by the dolphin to cover a distance of 114 km in downstream.
1. 4
2. 6
3. 8
4. 10
5. 12

Answer 1

Correct Answer - Option 2 : 6

Given:

Speed of Dolphin in still water = 15 km/h

Speed of the stream = 4 km/h

Distance covered in downstream = 114 km

Formulas Used:

Time = Distance/Speed

S_(downstream) = S_(boat) + S_(stream)

Calculation:

S_(downstream) = S_(boat) + S_(stream)

⇒ S_(downstream) = (15 + 4) km/h

⇒ S_(downstream) = 19 km/h

Time = Distance/Speed

⇒ T = 114/19 h

⇒ T = 6 h

∴ The time taken by dolphin to cover 114 km distance in downstream is 6 hours