The mass of 4 children, Emma, Marion, Fred and Reggie were taken. Only 3 children can be weighed at one time. Emma, Marion and Fred weighed a total of 118 kg. Marion, Fred and Reggie weighed a total of 87 kg. Emma, Fred and Reggie weighed a total of 102 kg. Emma, Marion, and Reggie weighed a total of 149 kg. What is the average mass of the 4 children?
Emma + Marion + Fred = 118 --- (1)
Marion + Fred + Reggie = 87 --- (2)
Emma + Fred + Reggie = 102 --- (3)
Emma + Marion + Reggie = 149 --- (4)

(1) + (2) + (3) + (4)
3(Emma + Marion + Fred + Reggie) = 118 + 87 + 102 + 149
3(Emma + Marion + Fred + Reggie) = 456
Emma + Marion + Fred + Reggie = 456 ÷ 3 = 152

Total mass of the 4 children = 152

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

Answer(s): 38 kg