The average weight of 15 men decreases by 2 kg when one of them, whose weight is 70 kg, is replaced by a new man. What is the weight of the new man (in kg)?

The new man weighs 40 kg.

The average of 15 men falls by 2 kg, so the total falls by 15 x 2 = 30 kg.

This drop equals the old weight minus the new weight.

New weight = 70 - 30.

70 - 30 = 40 kg.