The mass of 4 children, Emily, Yoko, Neave and Oliver were taken. Only 3 children can be weighed at one time. Emily, Yoko and Neave weighed a total of 53 kg. Yoko, Neave and Oliver weighed a total of 139 kg. Emily, Neave and Oliver weighed a total of 107 kg. Emily, Yoko, and Oliver weighed a total of 49 kg. What is the average mass of the 4 children?
Emily + Yoko + Neave = 53 --- (1)
Yoko + Neave + Oliver = 139 --- (2)
Emily + Neave + Oliver = 107 --- (3)
Emily + Yoko + Oliver = 49 --- (4)

(1) + (2) + (3) + (4)
3(Emily + Yoko + Neave + Oliver) = 53 + 139 + 107 + 49
3(Emily + Yoko + Neave + Oliver) = 348
Emily + Yoko + Neave + Oliver = 348 ÷ 3 = 116

Total mass of the 4 children = 116

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

Answer(s): 29 kg