Point A to Point B is a downstream journey of 300 km on a stream which flows at a speed of 5 km / hr . Two boats Pand 2 starts from point A and Point 3 respectively with speed of 25 km / hr and 15 km / hr in still water . After reaching the opposite point they return to their starting points , find after how much time will they meet second time ?
Answers
Given:
Distance of journey = 300km
Speed = 5km/hr
Speed of P = 25km/h
Speed of Q = 15km/h
To Find:
Time when they will meet second time
Solution:
Effective speed of boat P, when it starts from point A
= 25 + 5
= 30 km/hr ( As it travels downstream)
Effective speed of boat Q, when it starts from point B
= 15-5
= 10 km/hr ( As it travels upstream)
Therefore,
Relative Speed = Speed of P + Speed of Q
Relative speed = 30 + 10
= 40 km/hr
Time taken to meet first time = Distance / Speed
= 300 /40
= 7.5 hr
Now, to meet second time -
Effective speed of P = 30 km/hr
Effective speed of Q = 10 km/hr
Boat P is faster, thus -
300 / 30
=10 hr
In these 10 hrs, Q will moves a distance of 10×10 = 100 km
After 10 hours, both P and Q will be travelling upstream,
Speed of P = 20 km/hr
Speed of Q = 10 km/hr
Relative speed = 10km/hr
Time = distance / Speed
= 100/10 = 10
Total time = 10 + 10 = 20hrs.
Answer: The second time they will meet after 20 hrs.