Multiplying a 2-digit number by 39

Follow the Following Steps:

1. Select a 2-digit number.
2. Multiply by 4.
3. Add one zero.
4. Subtract the original number.

   Example:1

1. The 2-digit number chosen to multiply by 39 is 21.
2. Multiply by 4: 4 × 21 = 84.
3. Add one zero: 840.
4. Subtract the original number:
   840 - 21 = 819.
5. So 21 × 39 = 819.

Example:2

1. The 2-digit number chosen to multiply by 39 is 71.
2. Multiply by 4: 4 × 71 = 284.
3. Add one zero: 2840.
4. Subtract the original number:
   2840 - 71 = 2800 - 31 = 2769.
5. So 71 × 39 = 2769.