cross-multiplication technique - two 2- Digit number

 

"To multiply two 2-digit numbers
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.

EX 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).

Thought Process Summary

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EX 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).

Thought Process Summary