The mass of 4 children, Usha, Kimberly, Wesley and Ken were taken. Only 3 children can be weighed at one time. Usha, Kimberly and Wesley weighed a total of 94 kg. Kimberly, Wesley and Ken weighed a total of 111 kg. Usha, Wesley and Ken weighed a total of 87 kg. Usha, Kimberly, and Ken weighed a total of 56 kg. What is the average mass of the 4 children?
Usha + Kimberly + Wesley = 94 --- (1)
Kimberly + Wesley + Ken = 111 --- (2)
Usha + Wesley + Ken = 87 --- (3)
Usha + Kimberly + Ken = 56 --- (4)

(1) + (2) + (3) + (4)
3(Usha + Kimberly + Wesley + Ken) = 94 + 111 + 87 + 56
3(Usha + Kimberly + Wesley + Ken) = 348
Usha + Kimberly + Wesley + Ken = 348 ÷ 3 = 116

Total mass of the 4 children = 116

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

Answer(s): 29 kg