The mass of 4 children, Lynn, Gwen, Tom and Bryan were taken. Only 3 children can be weighed at one time. Lynn, Gwen and Tom weighed a total of 148 kg. Gwen, Tom and Bryan weighed a total of 107 kg. Lynn, Tom and Bryan weighed a total of 147 kg. Lynn, Gwen, and Bryan weighed a total of 66 kg. What is the average mass of the 4 children?
Lynn + Gwen + Tom = 148 --- (1)
Gwen + Tom + Bryan = 107 --- (2)
Lynn + Tom + Bryan = 147 --- (3)
Lynn + Gwen + Bryan = 66 --- (4)

(1) + (2) + (3) + (4)
3(Lynn + Gwen + Tom + Bryan) = 148 + 107 + 147 + 66
3(Lynn + Gwen + Tom + Bryan) = 468
Lynn + Gwen + Tom + Bryan = 468 ÷ 3 = 156

Total mass of the 4 children = 156

Average mass of the 4 children
= 156 ÷ 4
= 39

Answer(s): 39 kg