The mass of 4 children, Erika, Ivory, Tim and Harry were taken. Only 3 children can be weighed at one time. Erika, Ivory and Tim weighed a total of 118 kg. Ivory, Tim and Harry weighed a total of 146 kg. Erika, Tim and Harry weighed a total of 150 kg. Erika, Ivory, and Harry weighed a total of 126 kg. What is the average mass of the 4 children?
Erika + Ivory + Tim = 118 --- (1)
Ivory + Tim + Harry = 146 --- (2)
Erika + Tim + Harry = 150 --- (3)
Erika + Ivory + Harry = 126 --- (4)

(1) + (2) + (3) + (4)
3(Erika + Ivory + Tim + Harry) = 118 + 146 + 150 + 126
3(Erika + Ivory + Tim + Harry) = 540
Erika + Ivory + Tim + Harry = 540 ÷ 3 = 180

Total mass of the 4 children = 180

Average mass of the 4 children
= 180 ÷ 4
= 45

Answer(s): 45 kg