The mass of 4 children, Emma, Cindy, Nick and Dylan were taken. Only 3 children can be weighed at one time. Emma, Cindy and Nick weighed a total of 145 kg. Cindy, Nick and Dylan weighed a total of 47 kg. Emma, Nick and Dylan weighed a total of 119 kg. Emma, Cindy, and Dylan weighed a total of 121 kg. What is the average mass of the 4 children?
Emma + Cindy + Nick = 145 --- (1)
Cindy + Nick + Dylan = 47 --- (2)
Emma + Nick + Dylan = 119 --- (3)
Emma + Cindy + Dylan = 121 --- (4)

(1) + (2) + (3) + (4)
3(Emma + Cindy + Nick + Dylan) = 145 + 47 + 119 + 121
3(Emma + Cindy + Nick + Dylan) = 432
Emma + Cindy + Nick + Dylan = 432 ÷ 3 = 144

Total mass of the 4 children = 144

Average mass of the 4 children
= 144 ÷ 4
= 36

Answer(s): 36 kg