The mass of 4 children, Zoe, Mary, Warren and Tom were taken. Only 3 children can be weighed at one time. Zoe, Mary and Warren weighed a total of 59 kg. Mary, Warren and Tom weighed a total of 80 kg. Zoe, Warren and Tom weighed a total of 134 kg. Zoe, Mary, and Tom weighed a total of 111 kg. What is the average mass of the 4 children?
Zoe + Mary + Warren = 59 --- (1)
Mary + Warren + Tom = 80 --- (2)
Zoe + Warren + Tom = 134 --- (3)
Zoe + Mary + Tom = 111 --- (4)

(1) + (2) + (3) + (4)
3(Zoe + Mary + Warren + Tom) = 59 + 80 + 134 + 111
3(Zoe + Mary + Warren + Tom) = 384
Zoe + Mary + Warren + Tom = 384 ÷ 3 = 128

Total mass of the 4 children = 128

Average mass of the 4 children
= 128 ÷ 4
= 32

Answer(s): 32 kg