Question

Note the mobile number of any members of your family from four digits five digits and 6 digits number
By repeating the digits.
By not repeating the digits

Answer 1

Answer:

We have to find no. of ways for  making 4 digit number.

    - - - - first place has 8 ditis to be filled with

     Second place can be filled with 9 digits since repition is allowed

    Third place can be filled with 9 digits

       Fourth place can also be filled 9 digits

Thus, total no. of ways will be

                        =8\times 9\times9\times9=5832=8×9×9×9=5832

Similarly,We have to find no. of ways for  making 5 digit number.

 -  - - - - first place has 8 ditis to be filled with

           Second place can be filled with 9 digits since repition is allowed

           Third place can be filled with 9 digits

           Fourth place can also be filled 9 digits

          Fifth place can be filled with 9 digits

Thus, total no. of ways will be

                        =8\times 9\times9\times9\times9=52488=8×9×9×9×9=52488

Now,We have to find no. of ways for  making 4 digit number.

   - - - - - - first place has 8 ditis to be filled with

     Second place can be filled with 9 digits since repition is allowed

   Third place can be filled with 9 digits

    Fourth place can also be filled 9 digits

   Fifth place can filled with 9 digits

  Sixth place can be filled with 9 digits

   Thus, total no. of ways will be

                        =8\times 9\times9\times9\times9\times9=472392=8×9×9×9×9×9=472392