Multiplying two digit number by 18

1. Select a 2-digit number.
2. Multiply it by 2.
3. Add one zero.
4. Subtract the number obtained by multiplying by 2 from the last number.

Example:

1. The 2-digit number chosen to multiply by 18 is 28.
2. 28 × 2 = 56 (multiply by 2).
3. Add one zero: 560.
4. Subtract: 560 - 56 = 504.
5. So 18 × 28 = 504.