The mass of 4 children, Jen, Xuan, Pierre and Jenson were taken. Only 3 children can be weighed at one time. Jen, Xuan and Pierre weighed a total of 65 kg. Xuan, Pierre and Jenson weighed a total of 75 kg. Jen, Pierre and Jenson weighed a total of 84 kg. Jen, Xuan, and Jenson weighed a total of 124 kg. What is the average mass of the 4 children?
Jen + Xuan + Pierre = 65 --- (1)
Xuan + Pierre + Jenson = 75 --- (2)
Jen + Pierre + Jenson = 84 --- (3)
Jen + Xuan + Jenson = 124 --- (4)

(1) + (2) + (3) + (4)
3(Jen + Xuan + Pierre + Jenson) = 65 + 75 + 84 + 124
3(Jen + Xuan + Pierre + Jenson) = 348
Jen + Xuan + Pierre + Jenson = 348 ÷ 3 = 116

Total mass of the 4 children = 116

Average mass of the 4 children
= 116 ÷ 4
= 29

Answer(s): 29 kg