The mass of 4 children, Xylia, Irene, Sean and Howard were taken. Only 3 children can be weighed at one time. Xylia, Irene and Sean weighed a total of 95 kg. Irene, Sean and Howard weighed a total of 52 kg. Xylia, Sean and Howard weighed a total of 61 kg. Xylia, Irene, and Howard weighed a total of 140 kg. What is the average mass of the 4 children?
Xylia + Irene + Sean = 95 --- (1)
Irene + Sean + Howard = 52 --- (2)
Xylia + Sean + Howard = 61 --- (3)
Xylia + Irene + Howard = 140 --- (4)

(1) + (2) + (3) + (4)
3(Xylia + Irene + Sean + Howard) = 95 + 52 + 61 + 140
3(Xylia + Irene + Sean + Howard) = 348
Xylia + Irene + Sean + Howard = 348 ÷ 3 = 116

Total mass of the 4 children = 116

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

Answer(s): 29 kg