The mass of 4 children, Mary, Shannon, Warren and Sam were taken. Only 3 children can be weighed at one time. Mary, Shannon and Warren weighed a total of 123 kg. Shannon, Warren and Sam weighed a total of 127 kg. Mary, Warren and Sam weighed a total of 144 kg. Mary, Shannon, and Sam weighed a total of 122 kg. What is the average mass of the 4 children?
Mary + Shannon + Warren = 123 --- (1)
Shannon + Warren + Sam = 127 --- (2)
Mary + Warren + Sam = 144 --- (3)
Mary + Shannon + Sam = 122 --- (4)

(1) + (2) + (3) + (4)
3(Mary + Shannon + Warren + Sam) = 123 + 127 + 144 + 122
3(Mary + Shannon + Warren + Sam) = 516
Mary + Shannon + Warren + Sam = 516 ÷ 3 = 172

Total mass of the 4 children = 172

Average mass of the 4 children
= 172 ÷ 4
= 43

Answer(s): 43 kg