apbqcr is 6 digit number is divisible by 11 If |(a+b+c)−(p+q+r)| is 0 or multiple of 11 There is only one possible way |(9+2+1)−(7+5+0)|=0 a,b,c∈{9,2,1} and p,q,r∈{7,5,0} or a,b,c∈{7,5,0} and p,q,r∈{9,2,1} Number of 6 digits numbers =3!.3!+2.2!.3!=36+24=60