The mass of 4 children, Sabrina, Shannon, Tommy and Reggie were taken. Only 3 children can be weighed at one time. Sabrina, Shannon and Tommy weighed a total of 71 kg. Shannon, Tommy and Reggie weighed a total of 107 kg. Sabrina, Tommy and Reggie weighed a total of 102 kg. Sabrina, Shannon, and Reggie weighed a total of 104 kg. What is the average mass of the 4 children?
Sabrina + Shannon + Tommy = 71 --- (1)
Shannon + Tommy + Reggie = 107 --- (2)
Sabrina + Tommy + Reggie = 102 --- (3)
Sabrina + Shannon + Reggie = 104 --- (4)

(1) + (2) + (3) + (4)
3(Sabrina + Shannon + Tommy + Reggie) = 71 + 107 + 102 + 104
3(Sabrina + Shannon + Tommy + Reggie) = 384
Sabrina + Shannon + Tommy + Reggie = 384 ÷ 3 = 128

Total mass of the 4 children = 128

Average mass of the 4 children
= 128 ÷ 4
= 32

Answer(s): 32 kg