The mass of 4 children, Cathy, Jane, Liam and Brandon were taken. Only 3 children can be weighed at one time. Cathy, Jane and Liam weighed a total of 115 kg. Jane, Liam and Brandon weighed a total of 150 kg. Cathy, Liam and Brandon weighed a total of 118 kg. Cathy, Jane, and Brandon weighed a total of 49 kg. What is the average mass of the 4 children?
Cathy + Jane + Liam = 115 --- (1)
Jane + Liam + Brandon = 150 --- (2)
Cathy + Liam + Brandon = 118 --- (3)
Cathy + Jane + Brandon = 49 --- (4)

(1) + (2) + (3) + (4)
3(Cathy + Jane + Liam + Brandon) = 115 + 150 + 118 + 49
3(Cathy + Jane + Liam + Brandon) = 432
Cathy + Jane + Liam + Brandon = 432 ÷ 3 = 144

Total mass of the 4 children = 144

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

Answer(s): 36 kg