The mass of 4 children, Jane, Hazel, Oliver and Wesley were taken. Only 3 children can be weighed at one time. Jane, Hazel and Oliver weighed a total of 47 kg. Hazel, Oliver and Wesley weighed a total of 118 kg. Jane, Oliver and Wesley weighed a total of 77 kg. Jane, Hazel, and Wesley weighed a total of 142 kg. What is the average mass of the 4 children?
Jane + Hazel + Oliver = 47 --- (1)
Hazel + Oliver + Wesley = 118 --- (2)
Jane + Oliver + Wesley = 77 --- (3)
Jane + Hazel + Wesley = 142 --- (4)

(1) + (2) + (3) + (4)
3(Jane + Hazel + Oliver + Wesley) = 47 + 118 + 77 + 142
3(Jane + Hazel + Oliver + Wesley) = 384
Jane + Hazel + Oliver + Wesley = 384 ÷ 3 = 128

Total mass of the 4 children = 128

Average mass of the 4 children
= 128 ÷ 4
= 32

Answer(s): 32 kg