The mass of 4 children, Emily, Olivia, Dylan and Daniel were taken. Only 3 children can be weighed at one time. Emily, Olivia and Dylan weighed a total of 54 kg. Olivia, Dylan and Daniel weighed a total of 70 kg. Emily, Dylan and Daniel weighed a total of 85 kg. Emily, Olivia, and Daniel weighed a total of 103 kg. What is the average mass of the 4 children?
Emily + Olivia + Dylan = 54 --- (1)
Olivia + Dylan + Daniel = 70 --- (2)
Emily + Dylan + Daniel = 85 --- (3)
Emily + Olivia + Daniel = 103 --- (4)

(1) + (2) + (3) + (4)
3(Emily + Olivia + Dylan + Daniel) = 54 + 70 + 85 + 103
3(Emily + Olivia + Dylan + Daniel) = 312
Emily + Olivia + Dylan + Daniel = 312 ÷ 3 = 104

Total mass of the 4 children = 104

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

Answer(s): 26 kg