The mass of 4 children, Winnie, Usha, Gabriel and Glen were taken. Only 3 children can be weighed at one time. Winnie, Usha and Gabriel weighed a total of 136 kg. Usha, Gabriel and Glen weighed a total of 86 kg. Winnie, Gabriel and Glen weighed a total of 104 kg. Winnie, Usha, and Glen weighed a total of 70 kg. What is the average mass of the 4 children?
Winnie + Usha + Gabriel = 136 --- (1)
Usha + Gabriel + Glen = 86 --- (2)
Winnie + Gabriel + Glen = 104 --- (3)
Winnie + Usha + Glen = 70 --- (4)

(1) + (2) + (3) + (4)
3(Winnie + Usha + Gabriel + Glen) = 136 + 86 + 104 + 70
3(Winnie + Usha + Gabriel + Glen) = 396
Winnie + Usha + Gabriel + Glen = 396 ÷ 3 = 132

Total mass of the 4 children = 132

Average mass of the 4 children
= 132 ÷ 4
= 33

Answer(s): 33 kg