Amazing math! Forward to all your friends and you will be rewarded!

Factual Questions
1

[QUOTE=annoying coworker forward]
Here is a math trick so unbelievable that it will amaze you.

  1. Grab a calculator (you won’t be able to do this 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??
[/QUOTE]

How does this work?

2

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

3

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:

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

I beg to differ…

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

We have x

  1. Multiply by 80

80x

  1. Add 1

80x + 1

  1. Multiply by 250.

20000x + 250

  1. Add the last 4 digits of your phone number

20000x + y + 250

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

20000x + 2y + 250

  1. Subtract 250.

20000x + 2y

  1. Divide number by 2

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

4

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

5

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. :wink: )

6

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.

7

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.

8

[QUOTE=Rysto]

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

I beg to differ…

[/QUOTE]

Arrogant bastard*!

-Cem

*I am duly impressed.

9

[QUOTE=Rysto]
Now, 10000x is just x followed by four zeros. Adding y to it will make your phone number.
[/QUOTE]
Beautifully done.

10

[QUOTE=Cemetery Savior]
Arrogant bastard*!

-Cem

*I am duly impressed.
[/QUOTE]

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.