The mass of 4 children, Jane, Nicole, Howard and Eric were taken. Only 3 children can be weighed at one time. Jane, Nicole and Howard weighed a total of 136 kg. Nicole, Howard and Eric weighed a total of 133 kg. Jane, Howard and Eric weighed a total of 140 kg. Jane, Nicole, and Eric weighed a total of 131 kg. What is the average mass of the 4 children?
Jane + Nicole + Howard = 136 --- (1)
Nicole + Howard + Eric = 133 --- (2)
Jane + Howard + Eric = 140 --- (3)
Jane + Nicole + Eric = 131 --- (4)

(1) + (2) + (3) + (4)
3(Jane + Nicole + Howard + Eric) = 136 + 133 + 140 + 131
3(Jane + Nicole + Howard + Eric) = 540
Jane + Nicole + Howard + Eric = 540 ÷ 3 = 180

Total mass of the 4 children = 180

Average mass of the 4 children
= 180 ÷ 4
= 45

Answer(s): 45 kg