The mass of 4 children, Pamela, Xandra, Jenson and Rael were taken. Only 3 children can be weighed at one time. Pamela, Xandra and Jenson weighed a total of 130 kg. Xandra, Jenson and Rael weighed a total of 98 kg. Pamela, Jenson and Rael weighed a total of 128 kg. Pamela, Xandra, and Rael weighed a total of 88 kg. What is the average mass of the 4 children?
Pamela + Xandra + Jenson = 130 --- (1)
Xandra + Jenson + Rael = 98 --- (2)
Pamela + Jenson + Rael = 128 --- (3)
Pamela + Xandra + Rael = 88 --- (4)

(1) + (2) + (3) + (4)
3(Pamela + Xandra + Jenson + Rael) = 130 + 98 + 128 + 88
3(Pamela + Xandra + Jenson + Rael) = 444
Pamela + Xandra + Jenson + Rael = 444 ÷ 3 = 148

Total mass of the 4 children = 148

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

Answer(s): 37 kg