The mass of 4 children, Wendy, Victoria, Liam and Archie were taken. Only 3 children can be weighed at one time. Wendy, Victoria and Liam weighed a total of 131 kg. Victoria, Liam and Archie weighed a total of 73 kg. Wendy, Liam and Archie weighed a total of 124 kg. Wendy, Victoria, and Archie weighed a total of 68 kg. What is the average mass of the 4 children?
Wendy + Victoria + Liam = 131 --- (1)
Victoria + Liam + Archie = 73 --- (2)
Wendy + Liam + Archie = 124 --- (3)
Wendy + Victoria + Archie = 68 --- (4)

(1) + (2) + (3) + (4)
3(Wendy + Victoria + Liam + Archie) = 131 + 73 + 124 + 68
3(Wendy + Victoria + Liam + Archie) = 396
Wendy + Victoria + Liam + Archie = 396 ÷ 3 = 132

Total mass of the 4 children = 132

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

Answer(s): 33 kg