The mass of 4 children, Min, Raeann, Perry and Ian were taken. Only 3 children can be weighed at one time. Min, Raeann and Perry weighed a total of 79 kg. Raeann, Perry and Ian weighed a total of 99 kg. Min, Perry and Ian weighed a total of 67 kg. Min, Raeann, and Ian weighed a total of 79 kg. What is the average mass of the 4 children?
Min + Raeann + Perry = 79 --- (1)
Raeann + Perry + Ian = 99 --- (2)
Min + Perry + Ian = 67 --- (3)
Min + Raeann + Ian = 79 --- (4)

(1) + (2) + (3) + (4)
3(Min + Raeann + Perry + Ian) = 79 + 99 + 67 + 79
3(Min + Raeann + Perry + Ian) = 324
Min + Raeann + Perry + Ian = 324 ÷ 3 = 108

Total mass of the 4 children = 108

Average mass of the 4 children
= 108 ÷ 4
= 27

Answer(s): 27 kg