Going downstream (12 km/h in still water, current 3 km/h), Dinesh drops a water bottle overboard. He notices 20 minutes later, turns round and rows back with the same effort. How long after turning does he reach the bottle?

Question

Accepted Answer

20 minutes. Think relative to the water: the bottle is still and the boat moves at 12 km/h. In 20 min it gets 4 km from the bottle, so returning at 12 km/h also takes 20 minutes. The current's speed doesn't matter.

Going downstream (12 km/h in still water, current 3 km/h), Dinesh drops a water bottle overboard. He notices 20 minutes later, turns round and rows back with the same effort. How long after turning does he reach the bottle?

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