Math Trick - Multiplication of Two 2-Digit Numbers

To multiply two 2-digit numbers without showing work, first multiply the ones digits together, then 'cross-multiply,' and finally multiply the tens digits together.

Make sure to carry whenever a product exceeds 9. As you will see in the examples below, you must work your way from right to left to perform this trick.


Example 1: 12 x 23

1. Multiply the ones digits: 2x3=6 (ones digit answer).
2. Cross-multiply and add: (1x3)+(2x2)=7 (tens-digit answer).
3. Multiply the tens digits: 1x2=2 (hundreds-digit answer).
4. Combine: 276 (the answer).

Example 2: 31 x 24

1. Multiply the ones digits: 1x4=4 (ones digits answer).
2. Cross-multiply and add: (3x4)+(1x2)=14 (use the 4 as the tens-digit answer, and carry the 1).
3. Multiply the tens digits, and add the 1: (3x2)+1=7 (hundreds-digit answer).
4. Combine: 744 (the answer).

Note: 
This trick will also work on numbers with zeroes and decimal points. Also as you are cross-multiplying, it is generally easier to begin with the larger product and then add the smaller product.