The mass of 4 children, Kimberly, Zara, Neave and George were taken. Only 3 children can be weighed at one time. Kimberly, Zara and Neave weighed a total of 116 kg. Zara, Neave and George weighed a total of 145 kg. Kimberly, Neave and George weighed a total of 129 kg. Kimberly, Zara, and George weighed a total of 54 kg. What is the average mass of the 4 children?
Kimberly + Zara + Neave = 116 --- (1)
Zara + Neave + George = 145 --- (2)
Kimberly + Neave + George = 129 --- (3)
Kimberly + Zara + George = 54 --- (4)

(1) + (2) + (3) + (4)
3(Kimberly + Zara + Neave + George) = 116 + 145 + 129 + 54
3(Kimberly + Zara + Neave + George) = 444
Kimberly + Zara + Neave + George = 444 ÷ 3 = 148

Total mass of the 4 children = 148

Average mass of the 4 children
= 148 ÷ 4
= 37

Answer(s): 37 kg