Multiplying two digit number by 24

1. Select a 2-digit number.
2. Add two zeros to the number.
3. Divide it by 4.
4. From this, subtract the original number.

Example:

1. The 2-digit number chosen to multiply by 24 is 21.
2. Add two zeros: 2100.
3. Divide by 4: 2100/4 = 525.
4. Subtract the original number: 525 - 21 = 504.
5. So 21 × 24 = 504.