The mass of 4 children, Barbara, Xylia, Japheth and Pierre were taken. Only 3 children can be weighed at one time. Barbara, Xylia and Japheth weighed a total of 101 kg. Xylia, Japheth and Pierre weighed a total of 134 kg. Barbara, Japheth and Pierre weighed a total of 115 kg. Barbara, Xylia, and Pierre weighed a total of 46 kg. What is the average mass of the 4 children?
Barbara + Xylia + Japheth = 101 --- (1)
Xylia + Japheth + Pierre = 134 --- (2)
Barbara + Japheth + Pierre = 115 --- (3)
Barbara + Xylia + Pierre = 46 --- (4)

(1) + (2) + (3) + (4)
3(Barbara + Xylia + Japheth + Pierre) = 101 + 134 + 115 + 46
3(Barbara + Xylia + Japheth + Pierre) = 396
Barbara + Xylia + Japheth + Pierre = 396 ÷ 3 = 132

Total mass of the 4 children = 132

Average mass of the 4 children
= 132 ÷ 4
= 33

Answer(s): 33 kg