The mass of 4 children, Kimberly, Sabrina, Wesley and Eric were taken. Only 3 children can be weighed at one time. Kimberly, Sabrina and Wesley weighed a total of 87 kg. Sabrina, Wesley and Eric weighed a total of 88 kg. Kimberly, Wesley and Eric weighed a total of 68 kg. Kimberly, Sabrina, and Eric weighed a total of 117 kg. What is the average mass of the 4 children?
Kimberly + Sabrina + Wesley = 87 --- (1)
Sabrina + Wesley + Eric = 88 --- (2)
Kimberly + Wesley + Eric = 68 --- (3)
Kimberly + Sabrina + Eric = 117 --- (4)

(1) + (2) + (3) + (4)
3(Kimberly + Sabrina + Wesley + Eric) = 87 + 88 + 68 + 117
3(Kimberly + Sabrina + Wesley + Eric) = 360
Kimberly + Sabrina + Wesley + Eric = 360 ÷ 3 = 120

Total mass of the 4 children = 120

Average mass of the 4 children
= 120 ÷ 4
= 30

Answer(s): 30 kg