Question

In a river, a boat covers 8 km in 40 min while travelling downstream, but takes 1
to make the return journey. If the speed of the boat and the flow of the river ar
uniform, then the speed of the stream is
1) 2 km/h
2) 3 km/h
3) 4 km/h
4) 6 km/h​

Answer 1

Answer:

2 km/hr

Step-by-step explanation:

Let speed in still water be u and in moving water be v.

Downstream = u+v

Upstream = u-v

Distance is constant : 8km

Distance= Speed/Time

8km = u+v/40/60

8km = u+v/4/6

u+v = 12

u = 12-v

Similarly,

u-v/1 = 8km

u-v = 8

Substituting value of u.

12-v-v= 8

12-2v=8

2v=4

v=2