The mass of 4 children, Usha, Linda, Warren and Riordan were taken. Only 3 children can be weighed at one time. Usha, Linda and Warren weighed a total of 127 kg. Linda, Warren and Riordan weighed a total of 130 kg. Usha, Warren and Riordan weighed a total of 149 kg. Usha, Linda, and Riordan weighed a total of 62 kg. What is the average mass of the 4 children?
Usha + Linda + Warren = 127 --- (1)
Linda + Warren + Riordan = 130 --- (2)
Usha + Warren + Riordan = 149 --- (3)
Usha + Linda + Riordan = 62 --- (4)

(1) + (2) + (3) + (4)
3(Usha + Linda + Warren + Riordan) = 127 + 130 + 149 + 62
3(Usha + Linda + Warren + Riordan) = 468
Usha + Linda + Warren + Riordan = 468 ÷ 3 = 156

Total mass of the 4 children = 156

Average mass of the 4 children
= 156 ÷ 4
= 39

Answer(s): 39 kg