A man covers half of his journey at 6 km/h and the remaining

A man covers half of his journey at 6 km/h and the remaining half at 3 km/h. Find his average speed.

Given, A = 6 km/h, B = 3 km/ h
According to the formula, Average speed = 2AB/(A + B)
∴ Required average speed = 2 x 6 x 3/(6 + 3)
= 36/9 = 4 km/h