Whats your #??

[klnyc]

MATH PROBLEM (gotta try this)


Here is a math trick, so unbelievable that it will stump you.

Personally I would like to know who came up with this and why that person is not running the country.

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?

[Joshua312]

Now *that* is weird!

[TortoiseAWD]

Nifty trick. The math is pretty straightforward, though . . .

Let x be your three digit exchange, and y be the last four digits of the phone number:

2. Key in the first three digits of your phone number (NOT the area code).

There we have x

3. Multiply by 80.

80 * x

4. Add 1.

(80 * x) + 1

5. Multiply by 250.

250 * ( (80 * x) + 1 )

6. Add the last 4 digits of your phone number.

250 * ( (80 * x) + 1 ) + y

7. Add the last 4 digits of your phone number again.

250 * ( (80 * x) + 1 ) + y + y

8. Subtract 250.

250 * ( (80 * x) + 1 ) + y + y -250

9. Divide number by 2.

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

Simplify:
((200000x + 250) + y + y -250) / 2 =
(20000x + 250 + 2y - 250) / 2 =
(20000x + 2y)/2 =
10000x + y

Now substitute your three-digit exchange and four-digit number for x and y, and voila, mathmagic!

Tort

[Griz]

So you're telling me - I need to type in my phone number, to get my phone number back?

[TortoiseAWD]

Griz,

Well, that's how the original problem is set up. You at some point give your entire number (step 2, step 6); the calculations just obscure that.

Tort

[Griz]

Sorry, I should have denoted the sarcasm.

[TortoiseAWD]

Griz,

Sorry, I should have my sarcasm-meter tuned.

Tort

[PrinzII]

Interesting.....