The mass of 4 children, Victoria, Jade, Tommy and Andy were taken. Only 3 children can be weighed at one time. Victoria, Jade and Tommy weighed a total of 69 kg. Jade, Tommy and Andy weighed a total of 66 kg. Victoria, Tommy and Andy weighed a total of 150 kg. Victoria, Jade, and Andy weighed a total of 87 kg. What is the average mass of the 4 children?
Victoria + Jade + Tommy = 69 --- (1)
Jade + Tommy + Andy = 66 --- (2)
Victoria + Tommy + Andy = 150 --- (3)
Victoria + Jade + Andy = 87 --- (4)

(1) + (2) + (3) + (4)
3(Victoria + Jade + Tommy + Andy) = 69 + 66 + 150 + 87
3(Victoria + Jade + Tommy + Andy) = 372
Victoria + Jade + Tommy + Andy = 372 ÷ 3 = 124

Total mass of the 4 children = 124

Average mass of the 4 children
= 124 ÷ 4
= 31

Answer(s): 31 kg