The mass of 4 children, Diana, Dana, Dylan and Ahmad were taken. Only 3 children can be weighed at one time. Diana, Dana and Dylan weighed a total of 125 kg. Dana, Dylan and Ahmad weighed a total of 137 kg. Diana, Dylan and Ahmad weighed a total of 88 kg. Diana, Dana, and Ahmad weighed a total of 106 kg. What is the average mass of the 4 children?
Diana + Dana + Dylan = 125 --- (1)
Dana + Dylan + Ahmad = 137 --- (2)
Diana + Dylan + Ahmad = 88 --- (3)
Diana + Dana + Ahmad = 106 --- (4)

(1) + (2) + (3) + (4)
3(Diana + Dana + Dylan + Ahmad) = 125 + 137 + 88 + 106
3(Diana + Dana + Dylan + Ahmad) = 456
Diana + Dana + Dylan + Ahmad = 456 ÷ 3 = 152

Total mass of the 4 children = 152

Average mass of the 4 children
= 152 ÷ 4
= 38

Answer(s): 38 kg