A man swimming down stream overcome a flot at a point M. After travelling distance D he turned back and passed the float at a distance of D/2 from the point M. then the ratio of speed of swimmer with respect to still water to the speed of the speed of the river will be.

Let the swimmer's speed in still water be v and the river's speed be r, and let t be the time it takes the swimmer to travel distance D downstream. During this time t, the float drifts a distance of r times t, which must equal D divided by 2. Equating these gives r times t equals D divided by 2, meaning the float travels D divided by 2 while the swimmer travels D downstream. When the swimmer turns back, their net speed against the current is v minus r, giving a return time of D divided by (v minus r). The float continues to drift during this return time, and setting the total drift equal to D yields the equation D divided by r plus D divided by (v minus r) equals 2D divided by r. Solving this ratio equation results in the speed ratio v divided by r being 3. The result is 3.

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