The mass of 4 children, Cathy, Sabrina, Valen and David were taken. Only 3 children can be weighed at one time. Cathy, Sabrina and Valen weighed a total of 94 kg. Sabrina, Valen and David weighed a total of 147 kg. Cathy, Valen and David weighed a total of 51 kg. Cathy, Sabrina, and David weighed a total of 56 kg. What is the average mass of the 4 children?
Cathy + Sabrina + Valen = 94 --- (1)
Sabrina + Valen + David = 147 --- (2)
Cathy + Valen + David = 51 --- (3)
Cathy + Sabrina + David = 56 --- (4)

(1) + (2) + (3) + (4)
3(Cathy + Sabrina + Valen + David) = 94 + 147 + 51 + 56
3(Cathy + Sabrina + Valen + David) = 348
Cathy + Sabrina + Valen + David = 348 ÷ 3 = 116

Total mass of the 4 children = 116

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

Answer(s): 29 kg