Amusing puzzle

Miscellaneous and Personal Stuff I Must Share
1

Can you figure this out?

  1. Key into the calculator the first 3 digits of your phone number (not yourarea 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

The end result will be your phone number.

If you can figure this out, please explain how the arithmetic works

2

Note: this only works with US phone numbers.

3

Ooops!

4

x = the first 3 digits of your phone number
y = the last 4 digits of your phone number

To mathematically construct a 7 digit phone number out of x and y, use the equation 10000x + y. Now, to make sure the puzzle does the same thing:

  1. Put x into calculator
  2. Multiply by 80 (now we have 80x in calculator)
  3. Add 1 (80x + 1)
  4. Multiply by 250 (20000x + 250)
  5. Add y (20000x + 250 + y)
  6. Add y again (20000x + 250 + 2y)
  7. Subtract 250 (20000x + 2y)
  8. Divide by 2 (10000x + y)
    Success!

Does this answer your question?

5

Yes. Thank you, Algorithm.

6

My Canadian phone number worked!

Thats pretty cool though.

7

This has to be best correlation of username and post ever seen on this board.

8

Revtim, that’s exactly what I thought as well.

This is really neat, BTW. I’ll have to show my friends.

9

it worked on a UK phone number

10

Well, it works on any seven digit phone number (uh, though starting with 0 could be a problem.) If you rephrased “the first three digits” as “all but the last four digits” it would work for any phone number over four digits.