The mass of 4 children, Gem, Kimberly, Elijah and David were taken. Only 3 children can be weighed at one time. Gem, Kimberly and Elijah weighed a total of 82 kg. Kimberly, Elijah and David weighed a total of 65 kg. Gem, Elijah and David weighed a total of 127 kg. Gem, Kimberly, and David weighed a total of 134 kg. What is the average mass of the 4 children?
Gem + Kimberly + Elijah = 82 --- (1)
Kimberly + Elijah + David = 65 --- (2)
Gem + Elijah + David = 127 --- (3)
Gem + Kimberly + David = 134 --- (4)

(1) + (2) + (3) + (4)
3(Gem + Kimberly + Elijah + David) = 82 + 65 + 127 + 134
3(Gem + Kimberly + Elijah + David) = 408
Gem + Kimberly + Elijah + David = 408 ÷ 3 = 136

Total mass of the 4 children = 136

Average mass of the 4 children
= 136 ÷ 4
= 34

Answer(s): 34 kg