Many of us find it relatively easy to multiply by 2, 3, 5, and 10. If we can express our two-digit numbers as multiples of some of these numbers, then it will make multiplying them much easier.
Let’s start with a simple example: 12 x 18. We have all learned our multiplication tables up to 12, so let’s factor the 18 into 9 x 2.
Now we have the following:
12 x 18 = 12 x 9 x 2= 108 x 2
= 216
Another example is 24 x 21. Factoring 24 by 2 and 21 by 3, we can multiply as follows:
24 x 21 = 12 x 2 x 7 x 3
= 12 x 7 x 3 x 2 (Using the Commutative Property)
= 84 x 3 x 2
= 252 x 2
= 504
This takes some practice, but you’ll be amazed by what you can do if you give it a try!
