The mass of 4 children, Nicole, Emma, George and Tom were taken. Only 3 children can be weighed at one time. Nicole, Emma and George weighed a total of 63 kg. Emma, George and Tom weighed a total of 128 kg. Nicole, George and Tom weighed a total of 113 kg. Nicole, Emma, and Tom weighed a total of 128 kg. What is the average mass of the 4 children?
Nicole + Emma + George = 63 --- (1)
Emma + George + Tom = 128 --- (2)
Nicole + George + Tom = 113 --- (3)
Nicole + Emma + Tom = 128 --- (4)

(1) + (2) + (3) + (4)
3(Nicole + Emma + George + Tom) = 63 + 128 + 113 + 128
3(Nicole + Emma + George + Tom) = 432
Nicole + Emma + George + Tom = 432 ÷ 3 = 144

Total mass of the 4 children = 144

Average mass of the 4 children
= 144 ÷ 4
= 36

Answer(s): 36 kg