The mass of 4 children, Lynn, Tammy, David and Glen were taken. Only 3 children can be weighed at one time. Lynn, Tammy and David weighed a total of 107 kg. Tammy, David and Glen weighed a total of 133 kg. Lynn, David and Glen weighed a total of 119 kg. Lynn, Tammy, and Glen weighed a total of 73 kg. What is the average mass of the 4 children?
Lynn + Tammy + David = 107 --- (1)
Tammy + David + Glen = 133 --- (2)
Lynn + David + Glen = 119 --- (3)
Lynn + Tammy + Glen = 73 --- (4)

(1) + (2) + (3) + (4)
3(Lynn + Tammy + David + Glen) = 107 + 133 + 119 + 73
3(Lynn + Tammy + David + Glen) = 432
Lynn + Tammy + David + Glen = 432 ÷ 3 = 144

Total mass of the 4 children = 144

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

Answer(s): 36 kg