Divisibility Test

How many 5 digit multiples of 11 are there, if the digits 3,4,5,6,7 are in some order. I.e. the number is formed by these 5 digits without repetition.

12 20 22 None of these 8 11

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2 solutions

Kushal Bose
Aug 8, 2016

N = a b c d e N=a b c d e

To be divisible by it should satisfy ( a + c + e ) ( b + d ) = 11 k (a+c+e)-(b+d)=11 k

As, ( 7 + 6 + 5 ) ( 3 + 4 ) = 11 (7+6+5)-(3+4)=11

So, k k can be 0 , 1 0,1

Case(1) : k = 0 k=0

a + c + e = b + d a+c+e=b+d .These all numbers are in A.P. so sum of three can not be equal to sum of two.

Case(2): a + c + e b d = 11 a+c+e-b-d=11

This has only one solution i.e. ( a , c , e ) (a,c,e) can be 5 , 6 , 7 5,6,7 and ( b , d ) (b,d) can be ( 3 , 4 ) (3,4)

Taking permutations of these numbers total number of N is = 3 ! × 2 ! = 12 3! \times 2!=12

Thanks for making my work easy by posting otherwise I would post it tomorrow . I had the same solution, anyways +1...

Prince Loomba - 4 years, 10 months ago
Prince Loomba
Aug 8, 2016

class MyClass {

public static void main(String[ ] args) {


    for(int a=3;a<=7;a++){


      for(int b=3;b<=7;b++){if (a!=b){


         for(int c=3;c<=7;c++){if(b!=c && a!=c){


             for(int d=3;d<=7;d++){if(c!=d && b!=d){


            for(int e=3;e<=7;e++){if(d!=e && c!=e){


            if(a!=d && a!=e){


           if(b!=e){


String f=Integer.toString(a)+Integer.toString(b)+Integer.toString(c)+Integer.toString(d)+Integer.toString(e);


                  int s=Integer.parseInt(f);



              {if(s%11==0)



              {System.out.println(""+a+b+c+d+e);}}


         } 


        }


  }}}}


 } }


 }}




        }


       }


       }

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