The mass of 4 children, Emily, Zara, Nick and Luke were taken. Only 3 children can be weighed at one time. Emily, Zara and Nick weighed a total of 86 kg. Zara, Nick and Luke weighed a total of 57 kg. Emily, Nick and Luke weighed a total of 54 kg. Emily, Zara, and Luke weighed a total of 127 kg. What is the average mass of the 4 children?
Emily + Zara + Nick = 86 --- (1)
Zara + Nick + Luke = 57 --- (2)
Emily + Nick + Luke = 54 --- (3)
Emily + Zara + Luke = 127 --- (4)

(1) + (2) + (3) + (4)
3(Emily + Zara + Nick + Luke) = 86 + 57 + 54 + 127
3(Emily + Zara + Nick + Luke) = 324
Emily + Zara + Nick + Luke = 324 ÷ 3 = 108

Total mass of the 4 children = 108

Average mass of the 4 children
= 108 ÷ 4
= 27

Answer(s): 27 kg