The mass of 4 children, Cathy, Winnie, Cole and Andy were taken. Only 3 children can be weighed at one time. Cathy, Winnie and Cole weighed a total of 64 kg. Winnie, Cole and Andy weighed a total of 94 kg. Cathy, Cole and Andy weighed a total of 142 kg. Cathy, Winnie, and Andy weighed a total of 108 kg. What is the average mass of the 4 children?
Cathy + Winnie + Cole = 64 --- (1)
Winnie + Cole + Andy = 94 --- (2)
Cathy + Cole + Andy = 142 --- (3)
Cathy + Winnie + Andy = 108 --- (4)

(1) + (2) + (3) + (4)
3(Cathy + Winnie + Cole + Andy) = 64 + 94 + 142 + 108
3(Cathy + Winnie + Cole + Andy) = 408
Cathy + Winnie + Cole + Andy = 408 ÷ 3 = 136

Total mass of the 4 children = 136

Average mass of the 4 children
= 136 ÷ 4
= 34

Answer(s): 34 kg