I'm posting this in "Puzzle me this..." because I'm not sure
this "trick" is worthy of being considered "magic." It reeks
of math...and its conclusion (although mysterious) is
anticlimactic. But I'm sure some of you will find it quite
interesting.

Perhaps one of you can help me transform this into something
better. But first...a demo.
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Grab a pencil (pen), paper and calculator.
(A simple four function, eight digit readout calc.
works best. If you have something fancier, that's OK.
But the calculator on your cell phone will do just fine.)

Turn the calc. on and hit the CLEAR key.
You're now going to create a PIN. You can
write it down somewhere on your piece of paper...
or not. (It's not at all important that you
remember the PIN. You won't be asked to use it
again. But if you choose to keep track of all your steps,
please double-check these steps for accuracy before responding.)

My bank's ATM requires me to use a 4-digit PIN,
but I want a bit more security than that. So please
choose a 5-digit PIN.

Enter your PIN into the calculator.

Now multiply your PIN by the number of days in
a week. (We're working with the Gregorian Calendar throughout this
trick.)

Next multiply THAT product by the number of months
in a year.

(Your calc. should now be displaying a 6 or 7 digit
number.)

The number on your calc's screen will serve as
an "encryption number."

Now I want you to choose any date that has occurred/will occur
in your lifetime. (This works for any date between 01 Mar 1900
and 28 Feb 2100.)
On your paper, write down the day,
the month, and the year (1900-2099). Use all four
digits for the year. Use "little endian" format:
[D month YYYY] or [DD month YYYY].
(http://en.wikipedia.org/wiki/Calendar_date)

This format is common to the vast majority of the world's countries,
but it may seem strange to some of my fellow U.S. citizens. Examples
should make things crystal-clear:


31 January 2075 (NOT January 31 2075)
3 May 1956
16 Aug 1999

Circle this date on your paper. We're going to modify that date
before entering it into the calculator.

First, we need to turn the month name into a special
coded digit. Beneath the name of your month
write the digit that corresponds to that month
according to the following correspondence:
Jan-4
Feb-6
Mar-3
Apr-5
May-4
Jun-6
Jul-5
Aug-7
Sep-9
Oct-1
Nov-3
Dec-2

Second, IF your chosen date falls in a January or February, please subtract
1 from the year. Write the "reduced" year below the original year.
(If your chosen date falls in one of the other ten months of the year,
let it be.)

Now combine the digits of the (modified) date to form a
6 or 7 digit number. You simply run the modified date
numbers together to form one long string of digits.
Day digit(s)...followed by month digit...followed by
the four year digits (less one for Jan/Feb).


So: 19 Feb 1960 would become the 7-digit number
1961959. (Feb has been replaced with a 6...and 1960 was decremented to
1959.)

6 Sep 2076 would become the 6-digit number 692076. (Sep has been replaced with
a 9...and the year was not changed.)

Got it?
Recap: You've got a 6 or 7-digit number in the
calc. (There's no way I could know this number.)
You've got a date written on your paper. (There's
no way I could know this date.)
And you've encoded your date as a 6 or 7 digit number.

Okay. The hard work is done. That wasn't so bad, was it?
We have only a bit more work to do.

Add your encoded date number to the number already in
the calculator. Got it? If so, the calculator
should now be displaying the sum, a number that may
have up to 8 digits.

Even if you gave me this number, there's no way for
me to use it to figure out your original PIN...or
the date you have in mind. If I knew the PIN, I
could easily determine the date. If I knew the
date, I could easily determine the PIN. But since
I know neither....

One last calculator step. Divide the number on
your screen by 7. The calculator now displays
a string of digits. PM me the two digits immediately
preceding the decimal point and the digit that
immediately follows the decimal point.

(If the screen shows 1656042.1756, PM me the number
42.1
If the screen shows 1065106.27783747327, PM me the number
06.2
If the screen shows 456657 (a whole number), PM
me the number 57.0)

Do not PM your PIN...or the resulting encryption number...
or the date. Only PM the three requested digits.

But keep all the other info near your computer.

Stan Alger

Thank goodness I'm not a salesman.
I thank the very few who gave this a try.
I will continue to respond to PMs sent by any
future participants.

Stan

My number is 58.0

Please enlighten me with the how in addition to your answer.

BJM

BJM,

Check your PMs. (If you're logged in at the Café,
you'll see a box near the upper righthand corner
of this page notifying you that you have a Private
Message. Click on that box. I mention this
'cuz I see this is your very first post to the Café.)

Stan

I've received a sudden flurry of PMs with regard to this.
Strange. It was all but ignored when it was first posted.

Maybe students are just now getting back to their computers
after winter break.

Speaking of winter, there's supposed to be an ice-storm
headed my way. This means my power may go out. So if you
send a PM...and don't get a timely response, please be
patient.

Stan

Stan - that was quite clever. I can see how you get the answer, but not how you deduced my phone number at the same time.

Steve Martin,

You are a wild and crazy guy!