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### Question

The speed of a boat in still water, the upstream speed of the boat and the downstream speed of the boat form an A.P.(Arithmetic Progression) whose middle term is ${5/8}$. What is the speed of the boat in still water?

**A**

${5/8}$ units.

**B**

$1{6/7}$ units.

**C**

$2{1/10}$ units.

**D**

$2{9/10}$ units.

**Soln.**

**Ans: a**

Let the speed of the boat in still water be u and the speed of the stream be v. The three speeds are u - v, u and u + v. They are in an A.P. with a common difference equal to v, and u as its middle term. Since u is also the speed of the boat in still water, the required answer is: ${5/8}$.