“If you think dogs can’t count, try putting three dog biscuits in your pocket and then giving Fido only two of them.”
~Phil Pastoret
Today is Random Tidbit Tuesday at StoryChuck, where I post something I find strange but interesting.
It’s amazingly easy to multiply 11 by any two digit number if you use the following trick. Split the number apart, add them together, and stick the sum in the middle.
To illustrate. Let’s say you have 52 X 11
- Split 52 apart. 5 _ 2
- Add the 5 + 2 together: 5 + 2 = 7
- Put the 7 between the 5 and the 2. 5 7 2
- So 52 X 11 = 572
Super simple, huh? Now what happens if the number you add together is 10 or greater? It’s still pretty easy, you just need to add another step and bump the first digit by one.
So we’ll say we have 58 X 11
- Split 58 apart. 5 _ 8
- Add the 5 + 8 together: 5 + 8 = 13 (Oops, it’s bigger than 10, we put the 3 in the middle and remember to bump the first digit)
- Put the 3 (from 13) between the 5 and the 8. 5 3 8
- Remember to bump the first digit: 6 3 8
- 58 x 11 = 638
Here’s a couple more examples:
- 15 X 11 split apart: 1 _ 5
- Add 1 + 5. 6
- 15 X 11 = 165
- 94 X 11 spit apart: 9 _ 4
- Add 9 + 4. 13
- Put the 3 in between them: 9 3 4
- Increment the first digit: 1034
This simple trick makes multiplication by 11 a snap.