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Two places are 400 m apart in the river. Two boat (A and B) starts from both places at the same time towards each other. If boat A is going downstream then another one is going upstream. The speed of boat A and B are 90 km/hr and 54 km/hr respectively then find after how much time they meet each other.

Two places are 400 m apart in the river. Two boat (A and B) starts from both places at the same time towards each other. If boat A is going downstream then another one is going upstream. The speed of boat A and B are 90 km/hr and 54 km/hr respectively then find after how much time they meet each other. Correct Answer 10 sec

Given:

Distance = 400 km

Speed of boat A = 90 km/hr

Speed of boat B = 54 km/hr

Formula:

Relative speed = S1 + S2 (in case of opposite direction)

Distance = Relative speed × time

Speed of upstream = speed of the boat – the speed of stream

Speed of downstream = speed of boat + speed of stream

x km/hr = x × (5/18) m/sec.

Calculation:

Let the speed of stream be x m/s

Speed of boat A = 90 km/hr = 90 × (5/18) = 25 m/s

Speed of boat B = 54 km/hr = 54 × (5/18) = 15 m/s

⇒Speed of Boat A in downstream = 25 + x

⇒ Speed of Boat B in upstream = 15 – x

Distance = relative speed × time

⇒ 400 = × t

⇒ t = 400/40 = 10 seconds

∴ Both the boat meet after 10 seconds

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