The mass of 4 children, Jane, Vanessa, George and Jenson were taken. Only 3 children can be weighed at one time. Jane, Vanessa and George weighed a total of 74 kg. Vanessa, George and Jenson weighed a total of 81 kg. Jane, George and Jenson weighed a total of 137 kg. Jane, Vanessa, and Jenson weighed a total of 116 kg. What is the average mass of the 4 children?
Jane + Vanessa + George = 74 --- (1)
Vanessa + George + Jenson = 81 --- (2)
Jane + George + Jenson = 137 --- (3)
Jane + Vanessa + Jenson = 116 --- (4)

(1) + (2) + (3) + (4)
3(Jane + Vanessa + George + Jenson) = 74 + 81 + 137 + 116
3(Jane + Vanessa + George + Jenson) = 408
Jane + Vanessa + George + Jenson = 408 ÷ 3 = 136

Total mass of the 4 children = 136

Average mass of the 4 children
= 136 ÷ 4
= 34

Answer(s): 34 kg