The mass of 4 children, Erika, Risa, Howard and Nick were taken. Only 3 children can be weighed at one time. Erika, Risa and Howard weighed a total of 60 kg. Risa, Howard and Nick weighed a total of 100 kg. Erika, Howard and Nick weighed a total of 46 kg. Erika, Risa, and Nick weighed a total of 118 kg. What is the average mass of the 4 children?
Erika + Risa + Howard = 60 --- (1)
Risa + Howard + Nick = 100 --- (2)
Erika + Howard + Nick = 46 --- (3)
Erika + Risa + Nick = 118 --- (4)

(1) + (2) + (3) + (4)
3(Erika + Risa + Howard + Nick) = 60 + 100 + 46 + 118
3(Erika + Risa + Howard + Nick) = 324
Erika + Risa + Howard + Nick = 324 ÷ 3 = 108

Total mass of the 4 children = 108

Average mass of the 4 children
= 108 ÷ 4
= 27

Answer(s): 27 kg