Two fast ways to multiply by 9
Here are two quick ways to multiply 9 by any number 1 through 10. If you’re currently in the process of memorizing multiplication tables, these are both great techniques to help you with your 9s.
For the first technique, you’ll use your hands. Hold out your hands flat in front of you, then number your fingers from left to right. If you want to multiply 9 by 1, bend down your first finger (the left-most finger). Then you count the number of fingers still up on either side of the finger you bended down. Because there are 0 fingers to the left of the bent one, and 9 fingers to the right of the bent one, then 9*1=09, or 9*1=9. Or let’s take 9*2. You bend down your second finger, which leaves you with 1 finger to the left of that bent finger, and 8 fingers to the right of that bent finger. So 9*2=18. And this works for multiplying 9 by anything 1 all the way through 10, because you can bend down your first finger, all the way through your 10th finger.
The second technique is a little more mathy. If you want to multiply 9 by 7, you start with the 7, and you subtract 1 to get to 6. And 6 is now your first number. To get the second number, add from 6 back up to 9. Since the difference is 3, the second number is 3. So 9*7=63. Take another example and do 9*4. Subtract 1 from the 4 to get to 3, and 3 is your first number. Add from 3 back up to 9. The difference is 6, so your second number is 6, which means 9*4=36.