The mass of 4 children, Gillian, Nicole, Julian and Owen were taken. Only 3 children can be weighed at one time. Gillian, Nicole and Julian weighed a total of 60 kg. Nicole, Julian and Owen weighed a total of 100 kg. Gillian, Julian and Owen weighed a total of 49 kg. Gillian, Nicole, and Owen weighed a total of 55 kg. What is the average mass of the 4 children?
Gillian + Nicole + Julian = 60 --- (1)
Nicole + Julian + Owen = 100 --- (2)
Gillian + Julian + Owen = 49 --- (3)
Gillian + Nicole + Owen = 55 --- (4)

(1) + (2) + (3) + (4)
3(Gillian + Nicole + Julian + Owen) = 60 + 100 + 49 + 55
3(Gillian + Nicole + Julian + Owen) = 264
Gillian + Nicole + Julian + Owen = 264 ÷ 3 = 88

Total mass of the 4 children = 88

Average mass of the 4 children
= 88 ÷ 4
= 22

Answer(s): 22 kg