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### Question

The speed of a boat in still water is 56 km/h. It takes the same time to travel an upstream distance of 11 km as it takes to travel a downstream distance of 17 km. The rate of flow of the stream is?

**A**

12 km/h.

**B**

13 km/h.

**C**

11 km/h.

**D**

15 km/h.

**Soln.**

**Ans: a**

Let v km/h be the rate of flow of the stream. Upstream and downstream times are equal. So $11/{56 - v}$ = $17/{56 + v}$. Solving for v, or verifying by putting the given options one by one, we get v = 12 km/h.