Why Does This Work?

Garage Logic | 12-5-03 | self

[Aeronaut]

Phone Number Math Trick

It really works!

1 - Key into the calculator the first 3 digits of your phone number (not area code).

2 - Multiply by 80.

3 - Add 1.

4 - Multiply by 250.

5 - Add last 4 digits of your phone number.

6 - Add last 4 digits of your phone number again.

7 - Subtract 250.

8 - Lastly divide by 2.

Is this your phone number?

IF you can figure this out . . . explain how it works :)

[Aeronaut]

I can't figure it out, but it did work.

[PetroniDE]

I will explain soon.... It did work.... I think I know why.

[thoughtomator]

First 3 digits = X; last 4 = Y
Phone number = 10,000X + Y

(250*(80X+1) + 2Y - 250)/2 is then the expression of the steps indicated.

So our equation is
(250(80X+1)+ 2Y -250)/2 = 10,000X +Y

factoring this out brings us to
(20,000X + 250 + 2Y -250)/2 = 10,000X +Y

drop the 250s as they cancel each other out, and do the division:

10,000X + Y = 10,000X + Y


(I learned to do this math in 4th grade, if I remember correctly)

[4mycountry]

Cool! :)

[PetroniDE]

IT DOES WORK.... HERE'S WHY.

Step 1 is the first input. Call it "X".

Steps 2 through 4 result in the following. "Z" is the running total on your calculator.
Z = 20000 (X) + 250
The 20000 once divided by 2, simply adds five zeros to the phone number prefix and reserve the spaces for the phone number suffix.

Steps 5 and 6 simple added twice the suffix. Call the phone number suffix "Y".

Step 7 simply negates the 250 from the formula for Z above. This is window dressing.

Step 8 divides the total by 2. The 20000 becomes 10000 as explained above and the second suffix addition is eliminated (resulting in one net suffix addition).

[PetroniDE]

Took Freepers about 5 minutes (add three to typing response) to figure this out.

Post this on DU. Let's see how long it takes them to figure it out.

[the_devils_advocate_666]

"This doesn't matter to us because it is intuitively obvious. Only professional mathematicians bother to belabor the obvious."
    -- G. C. Rota

[the_devils_advocate_666]

Anyone who cannot cope with mathematics is not fully human. At best he is a tolerable subhuman who has learned to wear shoes, bathe and not make messes in the house.
    -- Lazarus Long, "Time Enough for Love"

[Aeronaut]

Post this on DU. Let's see how long it takes them to figure it out.

ROFL Spewing Fresca on my screen.

[PetroniDE]

My profession is not that different from "professional mathematician".

[PetroniDE]

I LOVE tricky math problems.

[elbucko]

I'd be more impressed if the problem did not ask one to enter ones complete phone number. The rest of the "problem" is just, as one poster claimed, "window dressing", fooling you into thinking that the correct number that was produced by the "formula" was esoteric in origin.

[elbucko]

-- Lazarus Long, "Time Enough for Love"

"Math: Gives you the ability to predict the future, if you know at least two present facts".
My father.

[Khurkris]

It works for me.

[LiteKeeper]

bump

[EuroFrog]

It didnt work for mine. Then again, my number is only 6 digits. All the numbers were there with a zero in the middle of it.

[EuroFrog]

I guess Im a tolerable subhuman!