Răspuns:
n=10;
Explicație pas cu pas:
ab : n = b r c ==> ab=n*b+c
bc : n = c r a ==> bc=n*c+a
ca : n = a r b ==> ca=n*a+b
ab+bc+ca = n(a+b+c) + a+b+c
10a+10b+10c+a+b+c = n(a+b+c) + a+b+c
10a+10b+10c=n(a+b+c)
10(a+b+c)=n(a+b+c)
n=10;
pt n=10 ==>
ab=10b+c=bc
bc=10c+a=ca
ca=10a+b=ab
==> a=b=c ==> abc=aaa=100a+10a+a=111a ==> multiplu de 111