The speed of a boat in still water is 10km/h and the speed of the stream is 3km/h. How much time (in hours) will it take to sail 39km downstream and then return immediately 28km upstream?
- A4
- B7
- C8
- D3
Solution & Step-by-step Explanation
Given:
Speed of the boat in still water (u) = 10km/h
Speed of the stream (v) = 3km/h
Downstream speed (D) = u+v=10+3=13km/h
Upstream speed (U) = u−v=10−3=7km/h
Time taken downstream=
D
Downstream Distance
=
13
39
=3 hours
Time taken upstream=
U
Upstream Distance
=
7
28
=4 hours
Total Time=3+4=7 hours
Speed of the boat in still water (u) = 10km/h
Speed of the stream (v) = 3km/h
Downstream speed (D) = u+v=10+3=13km/h
Upstream speed (U) = u−v=10−3=7km/h
Time taken downstream=
D
Downstream Distance
=
13
39
=3 hours
Time taken upstream=
U
Upstream Distance
=
7
28
=4 hours
Total Time=3+4=7 hours