The mass of 4 children, Barbara, Nicole, Oscar and John were taken. Only 3 children can be weighed at one time. Barbara, Nicole and Oscar weighed a total of 55 kg. Nicole, Oscar and John weighed a total of 105 kg. Barbara, Oscar and John weighed a total of 106 kg. Barbara, Nicole, and John weighed a total of 46 kg. What is the average mass of the 4 children?
Barbara + Nicole + Oscar = 55 --- (1)
Nicole + Oscar + John = 105 --- (2)
Barbara + Oscar + John = 106 --- (3)
Barbara + Nicole + John = 46 --- (4)

(1) + (2) + (3) + (4)
3(Barbara + Nicole + Oscar + John) = 55 + 105 + 106 + 46
3(Barbara + Nicole + Oscar + John) = 312
Barbara + Nicole + Oscar + John = 312 ÷ 3 = 104

Total mass of the 4 children = 104

Average mass of the 4 children
= 104 ÷ 4
= 26

Answer(s): 26 kg