The mass of 4 children, Winnie, Esther, Peter and Jenson were taken. Only 3 children can be weighed at one time. Winnie, Esther and Peter weighed a total of 53 kg. Esther, Peter and Jenson weighed a total of 78 kg. Winnie, Peter and Jenson weighed a total of 74 kg. Winnie, Esther, and Jenson weighed a total of 143 kg. What is the average mass of the 4 children?
Winnie + Esther + Peter = 53 --- (1)
Esther + Peter + Jenson = 78 --- (2)
Winnie + Peter + Jenson = 74 --- (3)
Winnie + Esther + Jenson = 143 --- (4)

(1) + (2) + (3) + (4)
3(Winnie + Esther + Peter + Jenson) = 53 + 78 + 74 + 143
3(Winnie + Esther + Peter + Jenson) = 348
Winnie + Esther + Peter + Jenson = 348 ÷ 3 = 116

Total mass of the 4 children = 116

Average mass of the 4 children
= 116 ÷ 4
= 29

Answer(s): 29 kg