Multiplying a 2-digit number by 10001
              and adding 21

   The product of a 2-digit number and 10,001 + 21 is:

1. the two digits,
2. two zeros,
3. the two digits,
4. add 21.

   Example: 29 x 10001 + 21

   1. 29 x 10001 = 290029
   2. 290029 + 21 = 290050

   Multiplying a 3-digit number by 10001
              and adding 201

   The product of a 3-digit number and 10,001 + 201 is:

1. the three digits,
2. one zero,
3. the three digits,
4. add 201.

   Example: 436 x 10001 + 201

   1. 437 x 10001 = 4370437
   2. 4370437 + 201 = 4370638

   Multiplying a 4-digit number by 10001
              and adding 2001

   The product of a 4-digit number and 10,001 + 2001 is:

1. the four digits, repeated once
2. add 2001.

Example: 6741 x 10001 + 2001

1. 6741 x 10001 = 67416741
2. 67416741 + 2001 = 67418742

Create variations by changing the number to be added or subtracted - just make the number an easy one to handle mentally.