The mass of 4 children, Zoe, Linda, Oliver and Bobby were taken. Only 3 children can be weighed at one time. Zoe, Linda and Oliver weighed a total of 114 kg. Linda, Oliver and Bobby weighed a total of 91 kg. Zoe, Oliver and Bobby weighed a total of 132 kg. Zoe, Linda, and Bobby weighed a total of 95 kg. What is the average mass of the 4 children?
Zoe + Linda + Oliver = 114 --- (1)
Linda + Oliver + Bobby = 91 --- (2)
Zoe + Oliver + Bobby = 132 --- (3)
Zoe + Linda + Bobby = 95 --- (4)

(1) + (2) + (3) + (4)
3(Zoe + Linda + Oliver + Bobby) = 114 + 91 + 132 + 95
3(Zoe + Linda + Oliver + Bobby) = 432
Zoe + Linda + Oliver + Bobby = 432 ÷ 3 = 144

Total mass of the 4 children = 144

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

Answer(s): 36 kg