Phone number math magic! Kind of cool.

[TheRob]

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. Should have your phone number.

After it is broken down a bit though, it's really quite simple to see how this works.

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

factor out the /2
125(80x + 1) + y -125 = 10000x + y

10000x + 125 + y - 125 = 10000x + y

10000x + y = 10000x + y

See? Easy.

 

[Argyle]

Sounds easy...but did not work for me!

 

[BSLU]

didn't work here.. off by 1306

 

[nutmegs]

Sounds easy...but did not work for me!

didn't work here.. off by 1306

These guys must have dysfuntional calculators or can't follow instructions cause it worked perfectly for me.

And thanks TR aka Will Hunting for the explanation as to why it works.

 

[Argyle]

Yes...I am a moron! It worked! My mistake was TR's wording! I added the last 4 numbers (ie - steps 6&7 - 1+2+3+4 rather than 1234+).

 

[BSLU]

there we go

 

[TheRob]

It should be noted in the problem explanation that x=first three digits and y=last four digits. Forgot to add that.