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A train of length 400 m is crossing a river bridge with the speed of 10 m / sec and a boat is also crossing the river, which is just below the bridge. The length of the bridge is 200 m and the length of the boat is 20 m, what should be the speed of the boat so that both will reach to the other side of the river at the same time (consider the boat is travelling in still water)?

A train of length 400 m is crossing a river bridge with the speed of 10 m / sec and a boat is also crossing the river, which is just below the bridge. The length of the bridge is 200 m and the length of the boat is 20 m, what should be the speed of the boat so that both will reach to the other side of the river at the same time (consider the boat is travelling in still water)? Correct Answer 3.67 m / sec

Given:

Train length = 400 m

Speed of train = 10 m / sec,

Length of the bridge = 200 m

Length of boat = 20 m

Formula used

Speed = Distance / Time

Calculation

Let speed of boat be x m / sec

Total distance, which need to travel by train to cross the bridge = 400 + 200 = 600 m

Distance, which need to travel by boat to cross the bridge = 200 + 20  = 220 m

As per the question, time taken by both train and boat to cross the river is same, hence

⇒ 600 / 10 = 220 / x

⇒ 60 = 220 / x

⇒ x = 3.67 m / sec

∴ Speed of boat is 3.67 m / sec

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