Question

A boat whose speed is 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream is ___ km/hr.

Answer 1

The speed of the stream is 5 km/hr.

Explanation:

- Let's assume that the speed of stream is = x km/h

- Speed of boat in still water v = 15 km/h

- Total time taken = 4 hour and 30 mins or 9/5 hrs

- Distance covered (one way) = 30 km/s

Then,

Speed of boat downstream =( 15 + x ) km/h

Time taken downstream = (30/15 + x ) hrs

As time = distance / speed

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

Time taken upstream =( 30/15 - x ) hrs

Now,

Total time taken = Time taken downstream + Time taken upstream

or, 9/2 = (30/15 + x ) + (30/15 - x )

or, x = 5 km/h

The speed of the stream is 5 km/h

I hope my answer helps