The mass of 4 children, Tammy, Mary, Vaidev and Oscar were taken. Only 3 children can be weighed at one time. Tammy, Mary and Vaidev weighed a total of 110 kg. Mary, Vaidev and Oscar weighed a total of 99 kg. Tammy, Vaidev and Oscar weighed a total of 80 kg. Tammy, Mary, and Oscar weighed a total of 59 kg. What is the average mass of the 4 children?
Tammy + Mary + Vaidev = 110 --- (1)
Mary + Vaidev + Oscar = 99 --- (2)
Tammy + Vaidev + Oscar = 80 --- (3)
Tammy + Mary + Oscar = 59 --- (4)

(1) + (2) + (3) + (4)
3(Tammy + Mary + Vaidev + Oscar) = 110 + 99 + 80 + 59
3(Tammy + Mary + Vaidev + Oscar) = 348
Tammy + Mary + Vaidev + Oscar = 348 ÷ 3 = 116

Total mass of the 4 children = 116

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

Answer(s): 29 kg