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2 places are 108 km apart and 2 boats start from both places at the same time towards each other, If one boat is going downstream then other are is going to upstream. After how much time will they meet each other if their speeds are 15 km/hr and 21 km/hr.

2 places are 108 km apart and 2 boats start from both places at the same time towards each other, If one boat is going downstream then other are is going to upstream. After how much time will they meet each other if their speeds are 15 km/hr and 21 km/hr. Correct Answer 3 hrs

Given:

2 places are apart by distance 108 km

Speed of boat 1 = 15 km/hr and Speed of boat 2 = 21 km/hour

Formulas used:

If the speed of the stream be y km/hour and speed of boat be x km/hour

Speed downstream = (x + y) km/hour

Speed upstream = (x - y) km/hour

Calculation:

Let the speed of the stream be y km/hour and both the boats meet after t hour.

Boat A is moving downstream with 15 km/h
Speed of boat A = (15 + y) km/hr

Since Boat is moving upstream with 21 km/h
Speed of boat B = (21 - y) km/hr

According to the question,
(15 + y) × t + (21 - y) × t = 108
⇒ 21t + 15t = 108

⇒ 36t = 108 or t = 3 hours

∴ They meet after 3 hours

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