Speed of stream is 4 km/hr and the speed of boat is 11 km/hr. In how much time will the boat cover a distance of 21 km upstream and 45 downstream ?
Answer & explanation
Correct answer: option 1
We know that,
Upstream Speed = Speed of boat - Speed of stream
Downstream Speed = Speed of boat + Speed of stream
We have,
Speed of stream = 4 km/hr.
Speed of boat = 11 km/hr.
Upstream Speed = 11 - 4 = 7 km/h
Upstream distance = 21 km
Time = 21/7 = 3 hrs
Downstream Speed = 11 + 4 = 15 km/h
Downstream distance = 45 km
Time = 45/15 = 3 hrs
Total time = 3 + 3 = 6 hrs