The mass of 4 children, Nicole, Jane, Asher and Mark were taken. Only 3 children can be weighed at one time. Nicole, Jane and Asher weighed a total of 78 kg. Jane, Asher and Mark weighed a total of 83 kg. Nicole, Asher and Mark weighed a total of 105 kg. Nicole, Jane, and Mark weighed a total of 106 kg. What is the average mass of the 4 children?
Nicole + Jane + Asher = 78 --- (1)
Jane + Asher + Mark = 83 --- (2)
Nicole + Asher + Mark = 105 --- (3)
Nicole + Jane + Mark = 106 --- (4)

(1) + (2) + (3) + (4)
3(Nicole + Jane + Asher + Mark) = 78 + 83 + 105 + 106
3(Nicole + Jane + Asher + Mark) = 372
Nicole + Jane + Asher + Mark = 372 ÷ 3 = 124

Total mass of the 4 children = 124

Average mass of the 4 children
= 124 ÷ 4
= 31

Answer(s): 31 kg