Shambhu swims a certain distance upstream in 7 hours, while he returns the same distance downstream in 5 hours. If the speed of the stream is 2 km/hr, then find the speed of Shambhu in still water.

Let Shambhu's speed in still water = v km/hr. Upstream speed = v - 2, downstream speed = v + 2. Distance is same, so 7(v - 2) = 5(v + 2). Expanding: 7v - 14 = 5v + 10. Therefore: 2v = 24, giving v = 12 km/hr. This tests the concept of relative speed in stream conditions where the boat's effective speed changes based on direction.