The mass of 4 children, Gillian, Emma, Seth and Xavier were taken. Only 3 children can be weighed at one time. Gillian, Emma and Seth weighed a total of 125 kg. Emma, Seth and Xavier weighed a total of 105 kg. Gillian, Seth and Xavier weighed a total of 150 kg. Gillian, Emma, and Xavier weighed a total of 64 kg. What is the average mass of the 4 children?
Gillian + Emma + Seth = 125 --- (1)
Emma + Seth + Xavier = 105 --- (2)
Gillian + Seth + Xavier = 150 --- (3)
Gillian + Emma + Xavier = 64 --- (4)

(1) + (2) + (3) + (4)
3(Gillian + Emma + Seth + Xavier) = 125 + 105 + 150 + 64
3(Gillian + Emma + Seth + Xavier) = 444
Gillian + Emma + Seth + Xavier = 444 ÷ 3 = 148

Total mass of the 4 children = 148

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

Answer(s): 37 kg