The mass of 4 children, Cindy, Marion, Vaidev and Valen were taken. Only 3 children can be weighed at one time. Cindy, Marion and Vaidev weighed a total of 77 kg. Marion, Vaidev and Valen weighed a total of 89 kg. Cindy, Vaidev and Valen weighed a total of 70 kg. Cindy, Marion, and Valen weighed a total of 76 kg. What is the average mass of the 4 children?
Cindy + Marion + Vaidev = 77 --- (1)
Marion + Vaidev + Valen = 89 --- (2)
Cindy + Vaidev + Valen = 70 --- (3)
Cindy + Marion + Valen = 76 --- (4)

(1) + (2) + (3) + (4)
3(Cindy + Marion + Vaidev + Valen) = 77 + 89 + 70 + 76
3(Cindy + Marion + Vaidev + Valen) = 312
Cindy + Marion + Vaidev + Valen = 312 ÷ 3 = 104

Total mass of the 4 children = 104

Average mass of the 4 children
= 104 ÷ 4
= 26

Answer(s): 26 kg