The mass of 4 children, Emily, Olivia, Oscar and Glen were taken. Only 3 children can be weighed at one time. Emily, Olivia and Oscar weighed a total of 110 kg. Olivia, Oscar and Glen weighed a total of 84 kg. Emily, Oscar and Glen weighed a total of 141 kg. Emily, Olivia, and Glen weighed a total of 85 kg. What is the average mass of the 4 children?
Emily + Olivia + Oscar = 110 --- (1)
Olivia + Oscar + Glen = 84 --- (2)
Emily + Oscar + Glen = 141 --- (3)
Emily + Olivia + Glen = 85 --- (4)

(1) + (2) + (3) + (4)
3(Emily + Olivia + Oscar + Glen) = 110 + 84 + 141 + 85
3(Emily + Olivia + Oscar + Glen) = 420
Emily + Olivia + Oscar + Glen = 420 ÷ 3 = 140

Total mass of the 4 children = 140

Average mass of the 4 children
= 140 ÷ 4
= 35

Answer(s): 35 kg