The mass of 4 children, Xylia, Elyse, Lee and Caden were taken. Only 3 children can be weighed at one time. Xylia, Elyse and Lee weighed a total of 150 kg. Elyse, Lee and Caden weighed a total of 148 kg. Xylia, Lee and Caden weighed a total of 131 kg. Xylia, Elyse, and Caden weighed a total of 99 kg. What is the average mass of the 4 children?
Xylia + Elyse + Lee = 150 --- (1)
Elyse + Lee + Caden = 148 --- (2)
Xylia + Lee + Caden = 131 --- (3)
Xylia + Elyse + Caden = 99 --- (4)

(1) + (2) + (3) + (4)
3(Xylia + Elyse + Lee + Caden) = 150 + 148 + 131 + 99
3(Xylia + Elyse + Lee + Caden) = 528
Xylia + Elyse + Lee + Caden = 528 ÷ 3 = 176

Total mass of the 4 children = 176

Average mass of the 4 children
= 176 ÷ 4
= 44

Answer(s): 44 kg