a,b(c)=(abc-ab)/90
b,c(a)=(bca-bc)/90
c,a(b)=(cab-ca)/90
abc-ab=100a+10b+c-10a-b=90a+9b+c
bca-bc=100b+10c+a-10b-c=90b+9c+a
cab-ca=100c+10a+b-10c-a=90c+9a+b
X=V(90a+9b+c+90b+9c+a+90c+9a+b)/90= V (100a+100b+100c)/90
X=V(100/90) xV(a+b+c)= V10/9xV(a+b+c)=[V10(a+b+c)]/3