What is the 11 finger trick and how does it work?

The 11 finger trick is a math trick where you can quickly multiply numbers by 11. To use the trick, you separate the digits of the number you want to multiply by 11, add the two digits together, and place the result in between the original digits. This works because 11 is the same as 10 1, so when you add the two digits together and place the result in between, you are essentially multiplying the original number by 10 and then adding the original number to it.