Multiplying a 2-digit number by 99

1. Select a 2-digit number.
2. Add two zeros to the number.
3. Subtract the original number from the second number.

   Example:

1. The 2-digit number chosen to multiply by 99 is 79.
2. Add two zeros: 7900.
3. Subtract the 2-digit number:
   7900 - 79 = 7900 - 80 + 1 = 7820 + 1 = 7821.
4. So 79 x 99 = 7821.

   See the pattern?

1. The 2-digit number chosen to multiply by 99 is 42.
2. Add two zeros: 4200.
3. Subtract the 2-digit number:
   4200 - 42 = 4200 - 40 - 2 = 4160 - 2 = 4158.
4. So 42 x 99 = 4158.