Multiples of nine

Learn your nine times facts up to ten!

Step 1 Using your tools

All you need are your hands,and five fingers on each hand or good substitutes

Comments

[purduecer]

Very cool, sir :-)

[kaiga]

thanks for commenting!

[asyrith]

I learned this from watching Prison Break! Yay, T-Bag

[PKM]

The way I do this in my head is:
- Subtract one from the number you are multiplying by, that's the number of tens (eg. 9 * 6 is fifty-something, 9 * 3 is twentysomething, etc.)
- Subtract the number of tens from 9 to get the ones (so if you have 5 tens, 9-5=4, so 9*6 is 54.)

Hey presto, a multiplication turned into two easy subtractions.

[Lithium Rain]

Yep, that's how I do it, only instead of subtracting from nine, I subtract the other number from 10.

On a slightly different note, have you ever noticed that 9 is the equivalent of 0 if you add up numbers with the goal of reducing to one? Like if you're adding house numbers, say 4578, 4+5=9 + (7+8=15), and 1+5 = 6 +9 = 15 and of course, 1+5=6.

[Kiteman]

This is exactly how I teach my less-able class to do their nines...

[cammel8]

ironically enough to do your nines you can also just write down the numbers 0 through nine on a piece of paper then right next to where you wrote 0 through 9 write 9 through 0.

0
1
2
3
4
5
6
7
8
9

then

0 9
1 8
2 7
3 6
4 5
5 4
6 3
7 2
8 1
9 0

then you have the nines table through ten
1x9 = 09
2x9 = 18
3x9 = 27
and so on....
then you don't even have to count just write then look....pretty simple

There is also a little trick you can do with multiples of 11... every one knows 0 through 9 is just double the number but after that you take the first number and that is the first number of the answer the last number is the last number of the answer and the middle number is the two added together

so 11x22 would be 242 and 11x18 would be 198

then if you get a number that is higher than 9 carry the number over to the next number on the left so...

11x99 would be 1089 because it would be 9 18 9 so you take the 1 off the 18 and add it to the number on the left so then it would be 10 8 9...

So any two digit number multiplied by 11 is easy to do in your head now try it yourself
11x27=???
11x55=???
11x47=???

works all the way to 99... hope this helps someone

[frollard]

Awesome visualizations - as your first picture suggests; it sucks if you've had a finger amputated in an accident :P

Another neat 9-trick

multiply any integer by 9...say
3 x 9 = 27........2+7= 9
3131 x 9 = 28179....2+8+1+7+9 = 27.........2+7=9!
195423672 x 9 = 1758813048....1+7+5+8+8+1+3+0+4+8=45.....4+5=9!
works for ANY integer factor of 9 so long as you long multiply, and dont round.

[Crash Plague]

I knew you could do this, but never really knew HOW. Nice trick, thanks, will prove to be useful. (not for me though, seeing as I am already taking advanced functions, lol)

[kaiga]

yeah it helped me a lot when i first learned multiplication.

[shooby]

Pretty neat trick.

[kaiga]

thanks!