**Given**

Width of river = 3km/h

the velocity of the boat =5km/hr

Time is taken for shortest path = 15 mins

**Find out**

We have to determine the velocity of the river stream.

**Solution**

Boat crosses a river of width 1 km by shortest path in 15 min

v = 1 km/15 min

We will convert km/h to m/s

To convert km/h to m/s we use formula

xkm/h = x X (5/28) m/s

Hence 1km/h

= (1000/15 x 60) x (18/5) km/h

=4kmh−1

Speed of river, vr=√52−42

=3kmh−1