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### Question

A boy goes to his school at an average speed of 6 km/h, and returns back at an average speed of 3 km/h. What is the average speed for the to and fro journey?

**A**

4 km/h.

**B**

5 km/h.

**C**

3 km/h.

**D**

$2{1/3}$ km/h.

**Soln.**

**Ans: a**

If u and v are the to and fro speeds, then the standard formula is ${2uv}/{u + v}$ = ${2 × 6 × 3}/{6 + 3}$ = 4 km/h.