The mass of 4 children, Tina, Elyse, Albert and Eric were taken. Only 3 children can be weighed at one time. Tina, Elyse and Albert weighed a total of 53 kg. Elyse, Albert and Eric weighed a total of 96 kg. Tina, Albert and Eric weighed a total of 63 kg. Tina, Elyse, and Eric weighed a total of 112 kg. What is the average mass of the 4 children?
Tina + Elyse + Albert = 53 --- (1)
Elyse + Albert + Eric = 96 --- (2)
Tina + Albert + Eric = 63 --- (3)
Tina + Elyse + Eric = 112 --- (4)

(1) + (2) + (3) + (4)
3(Tina + Elyse + Albert + Eric) = 53 + 96 + 63 + 112
3(Tina + Elyse + Albert + Eric) = 324
Tina + Elyse + Albert + Eric = 324 ÷ 3 = 108

Total mass of the 4 children = 108

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

Answer(s): 27 kg