How to beat a calculator adding numbers! (math tricks)
More fun with 9's
This trick is so simple and it has blown away everyone I've tried it on. I hope you have a lot of laughs over this one. This is how it works:
You challenge a friend or family member to a race adding numbers. They get to use a calculator and you don't. Here's how you set it up:
- Have them write a 5 digit number (minimum) on a piece of paper (tell them not to use 0 or any duplicate numbers).
- You take the paper and write your own five digit number underneath theirs.
- They write another five digit number under yours. You don't look at this number (yet).
- Take the paper from them and turn it over (writing down).
- Let them get ready with their calculator.
- Say "go", then turn over the paper and write the answer before they can add it up on the calculator.
- Oh, you want to know how to beat them? :)
When you write your number under theirs, make each column add up to 9. Example: they write 12345, you write (seemingly random numbers) 87654 underneath.
Then they write the third row of numbers under yours. Let's say they write 57263. When you write the answer, you simply start on the right, subtract a 1 from the last number in the third row (3 in this case), then copy the remaining numbers exactly, then put a 1 at the beginning of your number. So, your answer in this example would be 157262. Easy, huh?
Try it again. They write 62891. You would write 37108. Let's say they write 12345 in the last row. The answer would be 112344.
And when they finally get it added up on the calculator, they will see that you are correct. :)
This works on numbers with as many digits as you care to try. You can also extend the number of rows that are used.
If you use 5 rows, you must subtract 2 from the last number on the right, copy exactly the remaining numbers, then put the 2 at the beginning.
Using five rows is set up by having them write a number, then you write a number underneath that makes each column add up to 9, they write another number under yours, then you write another number underneath that makes their most recent number add up to nine, they write the final number, then you add it up.