SOLUTION: A man walks from his home to a town 6 km away at a speed of 4 km/h and returns home at a speed of 12 km/h what is man's average speed for the whole journey

Walking at the speed of 4 km/h, the man spends 1.5 hours to cover 6 kilometers.


For the way back, moving at the speed of 12 km/h, he spends 0.5 of an hour.


In all, he spends 1.5 hours + 0.5 of an hour = 2 hours to cover 6 + 6 = 12 kilometers.


It means that his average speed on the way "to there" and back is   = 6 kilometers per hour.

    Notice that the average speed in this case  "6 km/h" IS NOT the average of the partial speeds  4 km/h  and  12 km/h/