How does this work?

According to this, it’s just an application of commutativy, distributivity, and associativity.

( ( (nnn * 80) +1 ) 250 + mmmm + mmmm - 250 ) / 2

( nnn * 80 * 250 + 250 + mmmm * 2 - 250 ) /2

( nnn * 80 * 125 + mmmm )

nnn *10000 + mmmm

nnn0000 + mmmm

nnnmmmm

I assume that it gives your phone number back to you? Let x be the first three digits of your phone number, y be the last four:

- Grab a calculator (you won’t be able to do this in your head)

I beg to differ…

- Key in the first three digits of your phone number (not the area code).

We have x

- Multiply by 80

80x

- Add 1

80x + 1

- Multiply by 250.

20000x + 250

- Add the last 4 digits of your phone number

20000x + y + 250

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

20000x + 2y + 250

- Subtract 250.

20000x + 2y

- Divide number by 2

10000x + y

Now, 10000x is just x followed by four zeros. Adding y to it will make your phone number.

Thank you **rysto** for sparing me from having to type what you did in a slightly different format.

Call the 3-digit prefix of your phone number P, and the 4-digit suffix S.

Write that formula out algebraically:

( (80P + 1)*250 + S + S - 250 ) / 2

Reduce it to:

10000P + S, which will be your phone number, written out.

(I see others have answered on preview, but I’ll post it anyway. )

Thanks, peeps! It really is quite simple, I just couldn’t see it.

I’m usually able to figure these things out. I’m still contemplating eating berries with my jackrabbit form Djibouti.

Of course, there’s an assumption that a phone number is 7 digits long. This is true in Zone 1, but not necessarily true in other zones. For example, in Zone 61, local phone numbers have 8 digits, with a two-digit area code.

Arrogant bastard*!

-Cem

*I am duly impressed.

Beautifully done.

Well, it helps that I got to write out every step like that. I would have gotten lost trying to track things in my head.