The mass of 4 children, Jen, Risa, George and Jeremy were taken. Only 3 children can be weighed at one time. Jen, Risa and George weighed a total of 88 kg. Risa, George and Jeremy weighed a total of 134 kg. Jen, George and Jeremy weighed a total of 146 kg. Jen, Risa, and Jeremy weighed a total of 100 kg. What is the average mass of the 4 children?
Jen + Risa + George = 88 --- (1)
Risa + George + Jeremy = 134 --- (2)
Jen + George + Jeremy = 146 --- (3)
Jen + Risa + Jeremy = 100 --- (4)

(1) + (2) + (3) + (4)
3(Jen + Risa + George + Jeremy) = 88 + 134 + 146 + 100
3(Jen + Risa + George + Jeremy) = 468
Jen + Risa + George + Jeremy = 468 ÷ 3 = 156

Total mass of the 4 children = 156

Average mass of the 4 children
= 156 ÷ 4
= 39

Answer(s): 39 kg