Question 868886
Average the four given values


(x+y+z+40)/4 = 10


Then isolate x+y+z


(x+y+z+40)/4 = 10
x+y+z+40 = 10*4
x+y+z+40 = 40
x+y+z = 40-40
x+y+z = 0


Then divide this sum by 3 to average x,y,z


(x+y+z)/3 = 0/3
(x+y+z)/3 = 0


So they average out to 0.