The mass of 4 children, Kathy, Min, Warren and Ken were taken. Only 3 children can be weighed at one time. Kathy, Min and Warren weighed a total of 110 kg. Min, Warren and Ken weighed a total of 139 kg. Kathy, Warren and Ken weighed a total of 101 kg. Kathy, Min, and Ken weighed a total of 106 kg. What is the average mass of the 4 children?
Kathy + Min + Warren = 110 --- (1)
Min + Warren + Ken = 139 --- (2)
Kathy + Warren + Ken = 101 --- (3)
Kathy + Min + Ken = 106 --- (4)

(1) + (2) + (3) + (4)
3(Kathy + Min + Warren + Ken) = 110 + 139 + 101 + 106
3(Kathy + Min + Warren + Ken) = 456
Kathy + Min + Warren + Ken = 456 ÷ 3 = 152

Total mass of the 4 children = 152

Average mass of the 4 children
= 152 ÷ 4
= 38

Answer(s): 38 kg