# stupid math trick - via email

#### pclstyle

##### Platinum Member
Here is a math trick so unbelievable that it will stump you.

1. Grab a calculator. (you won't be able to do this one in your head; there should be one on your computer )

2. Key in the first three digits of your phone number (NOT YOUR AREA CODE)

3. Multiply by 80

5. Multiply by 250

8. Subtract 250

9. Divide number by 2.

CLIFFs: end result = phone number
Explanation? If it even warrants one.

#### shuan24

##### Platinum Member
lol its a simple algebra 'trick'

#### Safeway

##### Lifer
If the number is 550-1250, it works like this:

550 is entered, and in the multiplication, moved over 4 decimels and doubled -> 1000000. You then add 2 times that last 4 digits. 1250 x 2 = 2500. So you get 1002500/2 = 550 - 1250.

The add 1 is multiplied by 250, so when you subtract 250, you negate that.

#### JujuFish

##### Lifer
It'd be amazing if you never put in your phone number.

#### dullard

##### Elite Member
Let your phone number be xxx-yyyy, where xxx*10000 is your first three digits and yyyy is the last four digits.

Let X = xxx.

Let Y = yyyy.

Thus the math says to do this:
80*X
80*X+1
20000*X + 250
20000*X + 250 + Y
20000*X + 250 + 2*Y
20000*X + 2*Y
10000*X + Y

Well, gee wizz, we just went in one big circle. 10000*X IS defined as your first three digits and Y is your last 4 digits. The whole math thing is just there to confuse you.

Here is the exact same trick. Pick a number, ANY number. Add 1. Subtract 1. WOW YOU GOT YOUR NUMBER BACK, ITS MAGIC!!!! How did it know! The world is going to end!

##### Platinum Member
4 5 and 8 cancel eachother.

#### Safeway

##### Lifer
[(((550 * 80) + 1) * 250) + (2 * 1250) - 250] / 2

[(550 * 80 * 250) + 250 + (2 * 1250) - 250] / 2 ... the +250 and -250 cancel, and then the *2 and /2 and *80 cancelish

(550 * 40 * 250) + 1250 = 5500000 + 1250 = 550-1250

#### Howard

##### Lifer
ok i'll scan it up for you

#### reverend boltron

##### Senior member
Originally posted by: pclstyle
Here is a math trick so unbelievable that it will stump you.

1. Grab a calculator. (you won't be able to do this one in your head; there should be one on your computer )

2. Key in the first three digits of your phone number (NOT YOUR AREA CODE)

3. Multiply by 80

5. Multiply by 250

8. Subtract 250

9. Divide number by 2.

CLIFFs: end result = phone number
Explanation? If it even warrants one.

let x = first 3 digits of phone number
let u = last 4 digits of phone number

x*80= 80x

80x+1*250 = 20000x*250
20,000x+250 +u
20,000x+250+u+u=20,000x+250+2u
20,000x+250+2u-250=20,000x+2u
(20,000x+2u)/2 = 10,000x+u

meaning, if my number is 555-1211
then, 555*10000 = 555,0000.. and when I add the last four digits.. I get.. 555-1211

woah!!

#### Davan

##### Senior member
(For the purposes of this post, my phone # is 222-2222)

222
X 80
--------
17760
+1
--------
17761
*250
--------
4440250

So what did they do here. Really, all they did was find a fancy way to move the (222) up from the hundreds spot to the millions spot. The doubling and the addition of a single 250 was just smoke and mirrors to make the trick seem interesting. When I say added a 250 lets look at what they did. 80 X 250 = 20,000. 20,000 X 222 = 4,440,000. They could have just as easily made it 40X250=10,000 since 10,000 X 222 = 2220000 (or 222-0000), but that wouldnt have been nearly as impressive at the end. So they toss in the +1 before multiplying by 250 and that adds one more that they will subtract out at the end. They make it seem necessary but it isnt. If you take step 4 and step 8 out the end result will be the same.

After that its pretty straight forward. Since they multiplied the original number by 80 instead of 40, everything is doubled, so you have to add your last 4 digits in twice.

4440250
+ 2222
+ 2222
----------
4444694

Then you have a number that looks impressive (especially if you have a fancy 484-1249 phone number. However, if you look at it with a simple phone number you can see where the trick is. Then just remove the superfluous 250 they had us add in earlier -

4444694
-250
----------
4444444

And then take out the superfluous doubling they made us do earlier -

4444444
/ 2
----------
222-2222

and you have your phone number back.