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[numbers] Ask Metafilter: How is this lame maths Trick Possible? …
  1. Grab a calculator
  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

Neat Maths Trick with Telephone Numbers

This entry was posted on Monday, May 8th, 2006 at 10:39 am and is filed under Weird.

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3 Comments

I have a six digit number. It gave me my number plus 1 extra digit.

[posted by Brian at 12:55am on May 9 2006]

Doesn’t work for my 6 digit number either!

[posted by Jim at 1:10pm on May 9 2006]

Assume 9 digit number, x. Call first three characters a, last four b, so 10000a+b=z
Simplify equation given:
(((250(80a+1))+b+b)-250)/2= z
Multiply out 250(80a+1) fuction goes to
(20000a+250+2b-250)/2=z
Cancel out +/- 250
(20000a+2b)/2=z
Divide top and bottom by 2 goes to
10000a+b=z QED
Feel self satisfied, then click on the link and realise that someone else had already explained even more simply.

[posted by gusset at 6:33pm on May 9 2006]

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