The mass of 4 children, Yoko, Olivia, Sam and Luis were taken. Only 3 children can be weighed at one time. Yoko, Olivia and Sam weighed a total of 94 kg. Olivia, Sam and Luis weighed a total of 101 kg. Yoko, Sam and Luis weighed a total of 106 kg. Yoko, Olivia, and Luis weighed a total of 59 kg. What is the average mass of the 4 children?
Yoko + Olivia + Sam = 94 --- (1)
Olivia + Sam + Luis = 101 --- (2)
Yoko + Sam + Luis = 106 --- (3)
Yoko + Olivia + Luis = 59 --- (4)

(1) + (2) + (3) + (4)
3(Yoko + Olivia + Sam + Luis) = 94 + 101 + 106 + 59
3(Yoko + Olivia + Sam + Luis) = 360
Yoko + Olivia + Sam + Luis = 360 ÷ 3 = 120

Total mass of the 4 children = 120

Average mass of the 4 children
= 120 ÷ 4
= 30

Answer(s): 30 kg