The mass of 4 children, Shannon, Tina, Simon and Vincent were taken. Only 3 children can be weighed at one time. Shannon, Tina and Simon weighed a total of 101 kg. Tina, Simon and Vincent weighed a total of 140 kg. Shannon, Simon and Vincent weighed a total of 97 kg. Shannon, Tina, and Vincent weighed a total of 142 kg. What is the average mass of the 4 children?
Shannon + Tina + Simon = 101 --- (1)
Tina + Simon + Vincent = 140 --- (2)
Shannon + Simon + Vincent = 97 --- (3)
Shannon + Tina + Vincent = 142 --- (4)

(1) + (2) + (3) + (4)
3(Shannon + Tina + Simon + Vincent) = 101 + 140 + 97 + 142
3(Shannon + Tina + Simon + Vincent) = 480
Shannon + Tina + Simon + Vincent = 480 ÷ 3 = 160

Total mass of the 4 children = 160

Average mass of the 4 children
= 160 ÷ 4
= 40

Answer(s): 40 kg