The mass of 4 children, Min, Erika, Rael and Mark were taken. Only 3 children can be weighed at one time. Min, Erika and Rael weighed a total of 92 kg. Erika, Rael and Mark weighed a total of 130 kg. Min, Rael and Mark weighed a total of 56 kg. Min, Erika, and Mark weighed a total of 142 kg. What is the average mass of the 4 children?
Min + Erika + Rael = 92 --- (1)
Erika + Rael + Mark = 130 --- (2)
Min + Rael + Mark = 56 --- (3)
Min + Erika + Mark = 142 --- (4)

(1) + (2) + (3) + (4)
3(Min + Erika + Rael + Mark) = 92 + 130 + 56 + 142
3(Min + Erika + Rael + Mark) = 420
Min + Erika + Rael + Mark = 420 ÷ 3 = 140

Total mass of the 4 children = 140

Average mass of the 4 children
= 140 ÷ 4
= 35

Answer(s): 35 kg