The mass of 4 children, Joelle, Hazel, Michael and Jack were taken. Only 3 children can be weighed at one time. Joelle, Hazel and Michael weighed a total of 135 kg. Hazel, Michael and Jack weighed a total of 95 kg. Joelle, Michael and Jack weighed a total of 111 kg. Joelle, Hazel, and Jack weighed a total of 103 kg. What is the average mass of the 4 children?
Joelle + Hazel + Michael = 135 --- (1)
Hazel + Michael + Jack = 95 --- (2)
Joelle + Michael + Jack = 111 --- (3)
Joelle + Hazel + Jack = 103 --- (4)

(1) + (2) + (3) + (4)
3(Joelle + Hazel + Michael + Jack) = 135 + 95 + 111 + 103
3(Joelle + Hazel + Michael + Jack) = 444
Joelle + Hazel + Michael + Jack = 444 ÷ 3 = 148

Total mass of the 4 children = 148

Average mass of the 4 children
= 148 ÷ 4
= 37

Answer(s): 37 kg