The mass of 4 children, Shiyun, Olivia, Mark and Bobby were taken. Only 3 children can be weighed at one time. Shiyun, Olivia and Mark weighed a total of 134 kg. Olivia, Mark and Bobby weighed a total of 109 kg. Shiyun, Mark and Bobby weighed a total of 132 kg. Shiyun, Olivia, and Bobby weighed a total of 69 kg. What is the average mass of the 4 children?
Shiyun + Olivia + Mark = 134 --- (1)
Olivia + Mark + Bobby = 109 --- (2)
Shiyun + Mark + Bobby = 132 --- (3)
Shiyun + Olivia + Bobby = 69 --- (4)

(1) + (2) + (3) + (4)
3(Shiyun + Olivia + Mark + Bobby) = 134 + 109 + 132 + 69
3(Shiyun + Olivia + Mark + Bobby) = 444
Shiyun + Olivia + Mark + Bobby = 444 ÷ 3 = 148

Total mass of the 4 children = 148

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

Answer(s): 37 kg