Question

A boat can travel at a speed of 12 km/hr in still water. If the speed of the stream is 8 km/hr, find the time taken by the boat to travel 60 km downstream.

• A. 5 hrs
• B. 3 hrs
• C. 2 hrs
• D. 15 hrs

Answer 1

The correct option is B

3 hrs

Consider, a boat moving at a speed of S1 and the speed of the water stream is S2.

If the stream and boat are moving in the same direction(Downstream or along the stream), the Effective speed of the boat = S1 + S2

And, If the stream and boat are moving in the opposite direction(Upstream or against the stream), the Effective speed of the boat = S1 - S2

Here, its downstream, so, Effective speed of the boat = 12 + 8 = 20 km/hr

And distance to be covered = 60 km

Time = Distance/ Speed

So, Time taken to cover 60 km$=\frac{60}{20}=3hrs$