A boat travels upstream from B to A and downstream from A to B in 3 hours. If the speed of the boat in still water is 9km/hr and the speed of the current is 3 km/hr the distance between A and B is?

4 km
6 km
8 km
12 km

Correct Answer: 12 km

Explanation:

Speed downstream = (9 + 3) km/hr = 12km/hr
Speed upstream = = (9 - 3) km/hr = 6km/hr
Let the distance AB = d km
Then, d/6 + d/12 = 3
⇒ 2d + d = 36
⇒ d = 12
∴ Distance AB = 12 km

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