Amazing Math Trick
 

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)
2. Key in the first three digits of your phone number (NOT the area code)
3. Multiply by 80
4. Add 1
5. Multiply by 250
6. Add the last 4 digits of your phone number
7. Add the last 4 digits of your phone number again.
8. Subtract 250
9. Divide number by 2

Do you recognize the answer?

it works lol

Neat.

lol, now that was neat. :)

Whoah...now why does that work?

x is first few digits, y is last few digits

80x+1
(80x+1)*250 = 20000x+250
20000x+250+y
20000x+250+y+y=20000x+250+2y
20000x+250+2y-250=20000x+2y
(20000x+2y)/2=10000x+y

That makes sense, huh. Given that the phone number is the last four digits plus 10,000 times the first three digits (because it is 4 decimal places over).

-Frikkle :tu:

WOW that was nice :)

x = (x1 * 80) + 1 * 250 + x2 + x2 - 250 / 2

wow cool. Thanks for sharing :)

Originally Posted by Frikkle

80x+1 (80x+1)*250 = 20000x+250 20000x+250+y 20000x+250+y+y=20000x+250+2y 20000x+250+2y-250=20000x+2y (20000x+2y)/2=10000x+y

Oh, why didn't you just say that in the first place? :lol:

:lol: works.

Wow. It even works with a hong kong phone number.

x = (x1 * 80) + 1 * 250 + x2 + x2 - 250 / 2

Is there a shorter mathematical expression for this? Or is that the shortest possible?

wont work if either in your last 4 digits, or the first 3 digits...the FIRST number is "0"
for example my last 4 digits were "0486" so it didnt work

Originally Posted by dgridley

x = (x1 * 80) + 1 * 250 + x2 + x2 - 250 / 2 Is there a shorter mathematical expression for this? Or is that the shortest possible?

This one is shorter: x = your phone number.

Originally Posted by unknowngiver

wont work if either in your last 4 digits, or the first 3 digits...the FIRST number is "0" for example my last 4 digits were "0486" so it didnt work

You did something wrong. (I tried it with xxx-0486 and it worked.) The only way it wouldn't "work" would be if the very first number is 0 which it can't be (I think).

That's Pretty Cool.

If you let x = first digits of phone number, y = last 4 digits of phone number.
[(80x + 1)250 + 2y - 250]/2
[20000x + 250 -250 + 2y]/2
[20000x + 2y]/2
10000x + y

So this does make sense, since you are effectively shifting your x value by a factor of 10000 or 4 zero places. This is similar to how a computer does addition and subtraction back in the old days when memory was at a premium.

Of course any leading zeros in the x place would make this equation produce the wrong result. Maybe that's why all phone numbers don't begin with zeros. :hehe:

Originally Posted by dgridley

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) 2. Key in the first three digits of your phone number (NOT the area code) 3. Multiply by 80 4. Add 1 5. Multiply by 250 6. Add the last 4 digits of your phone number 7. Add the last 4 digits of your phone number again. 8. Subtract 250 9. Divide number by 2 Do you recognize the answer?

Pretty cool! Gave me a chuckle.

And who would find the time to discover an equation like this?

-Commes

Nice! :)