Rowing at 8KM/hr in still water, Rima and Bhanu take 16h to row 39Km down a river and 39 Km .Find the speed?

Question

Rowing at 8KM/hr in still water, Rima and Bhanu take 16h to row 39Km down a river and 39 Km back.Find the speed of the current to two decimals

Answer 1

This problem asks you to find what component of speed was that of the river. You are given the distance covered and the time it took to cover it. You are also given an idea of what the speed component of the rowers would be.

So, determine the speed that the combined speeds (rowers and river) was by dividing the distance traveled by the time it took to travel it. That gives you the combined speed. Then subtract the speed the rowers added to find the speed of the river current.

Answer 2

Their speed downriver is 8+x km/hr
Their speed upriver is 8-x km/hr

39/(8+x) is the time it took downriver
39/(8-x) is the time it took upriver

39/(8+x) + 39/(8-x) = 16 hr
multiply each term by (8+x)(8-x)
39(8-x) + 39(8+x) = 16(8-x)(8+x)
312 - 39x + 312 + 39x = 16(64 - x^2)
624 = 1024 - 16x^2
16x^2 = 400
x^2 = 25
x = 5.00 km/hr (speed of the water)