The mass of 4 children, Min, Xylia, Julian and Sean were taken. Only 3 children can be weighed at one time. Min, Xylia and Julian weighed a total of 47 kg. Xylia, Julian and Sean weighed a total of 111 kg. Min, Julian and Sean weighed a total of 47 kg. Min, Xylia, and Sean weighed a total of 143 kg. What is the average mass of the 4 children?
Min + Xylia + Julian = 47 --- (1)
Xylia + Julian + Sean = 111 --- (2)
Min + Julian + Sean = 47 --- (3)
Min + Xylia + Sean = 143 --- (4)

(1) + (2) + (3) + (4)
3(Min + Xylia + Julian + Sean) = 47 + 111 + 47 + 143
3(Min + Xylia + Julian + Sean) = 348
Min + Xylia + Julian + Sean = 348 ÷ 3 = 116

Total mass of the 4 children = 116

Average mass of the 4 children
= 116 ÷ 4
= 29

Answer(s): 29 kg