Geeky math thing

[Celebration]

I'm a little bit of a numbers freak, and I heard this one from "The Human Calculator." My husband liked it so maybe you guys will too.

Tell someone to pick any two digit number. Then, in their head, they should add the two digits together. If the answer is still two digits, add those digits together, until they come down to one digit.

From the original number that they selected, subract the one digit number they calculated.

Then, with that answer, add those digits together.

Then, say to them--"The answer is nine." It turns out to be nine every single time.

For instance, suppose you chose 76

7+6=13

1+3=4

76-4=72

7+2=9

There you have it. Works with every single number.

[NMDemDist2]

1. 9 is a handy number

if your columns don't balance in a spreadsheet and the number you are 'off' is divisible by 9 you have a transposed number in your data somewhere

[pokerfan]

4. "Casting out the nines"

I believe it's called.

[OPERATIONMINDCRIME]

2. Here's My Math Trick Thing I've Always Used, And Even Used To Use It To Make Money.

It's squaring any two digit number in your head. I used to bet people 5 bucks at parties that I could square any two digit number in my head faster than they could do it on a calculator. For those who are first starting out, say faster than you can do it on paper. The way I do it is by using the algebraic formula (a+b)(a+b), which comes out to A squared + 2AB + B squared. Using that, I turn the the two digit number into two numbers and place them into the equation.

For example, to pick any random two digit number, let's say 72. That would be 70 + 2 squared. (70+2)(70+2) = 70 squared + 2*70*2 + 2 squared.

Breaking it out like that, it becomes easy (if you can retain numbers in your head). 70x70 = 4900 + 2*70(140)*2(280) = 5180 + 2*2(4) = 5184.

Practice a few times and once you get the hang of it, it's sure to impress!

[Celebration]

3. Got it!

Well, everything but retaining numbers in my head. I was always awful at "Concentration" (card game), and never could count suits in bridge. What would that be? Random access memory problem? My computing is fine at least.

That is great that it made you money. My claim to fame is that I can do mirror writing very quickly, in script, too. Hard to demonstrate here. I learned it for fun when I had a twisted mind in elementary school--doodling while the teacher talked, etc.

[pokerfan]

5. That's the way I've always done it

There are other cheats as well depending on the numbers involved.

On a recent Law and Order episode (the fake flu vaccine) McCoy pursued a sentence of 15 years to be served consecutively for each of the 16 counts of manslaughter.

I did it quickly by multiplying 16 by 10 to get 160. Five is half of ten. Half of 160 is 80. 160 plus 80 is 240.

When multiplying a large number by five it's usually easier to just multiply by ten and then take half of the result.

[Dr. Strange]

6. Here's a website game that's based on the same principle:

http://www.digicc.com/fido/