The mass of 4 children, Pamela, Roshel, Sean and Tommy were taken. Only 3 children can be weighed at one time. Pamela, Roshel and Sean weighed a total of 79 kg. Roshel, Sean and Tommy weighed a total of 141 kg. Pamela, Sean and Tommy weighed a total of 100 kg. Pamela, Roshel, and Tommy weighed a total of 112 kg. What is the average mass of the 4 children?
Pamela + Roshel + Sean = 79 --- (1)
Roshel + Sean + Tommy = 141 --- (2)
Pamela + Sean + Tommy = 100 --- (3)
Pamela + Roshel + Tommy = 112 --- (4)

(1) + (2) + (3) + (4)
3(Pamela + Roshel + Sean + Tommy) = 79 + 141 + 100 + 112
3(Pamela + Roshel + Sean + Tommy) = 432
Pamela + Roshel + Sean + Tommy = 432 ÷ 3 = 144

Total mass of the 4 children = 144

Average mass of the 4 children
= 144 ÷ 4
= 36

Answer(s): 36 kg