Math puzzle: 

If you are a car dealer, and know that sometimes people will pay cash
for a car using federal reserve note denominations of 1000, what
amounts of money must you seal into 10 marked envelopes so that you
can guarantee that no matter what the vehicle purchase price, you will
be able to give exact change without having to open an envelope?
Assume that the sale price is rounded to the nearest dollar and cents
are not used.  This is important, because you may have a less than
savory sales staff that might dip into the envelopes if they weren't
sealed, marked, and carefully accounted for.

Hi caseykangas:

The answer is quite straightforward. The amounts that should be in the
10 sealed envelopes are:

$1
$2
$4
$8
$16
$32
$64
$128
$256
$512

This is basically 2^0 through 2^9. With those 10 amounts, you can add
to make any dollar amount between $1 and $1000.

How to figure out which envelopes to give for change:

* Use the following online decimal to binary conversion tool to find
the binary representation.

http://acc6.its.brooklyn.cuny.edu/~gurwitz/core5/nav2tool.html

* Read the digits from right to left. If there's a 0 in the rightmost
spot, then the $1 envelope is not given as change. If there's a 1 in
the rightmost spot the $1 envelope is given as change. Similarly, the
second digit from the right corresponds to whether the $2 envelope is
given. And so on.

Example: Change = $754

754 (decimal) = 1011110010 (binary)

Therefore, you give the $2, $16, $32, $64, $128, and $512 envelopes.

2+16+32+64+128+512 = 754

Search Strategy (on Google):
* convert decimal binary

Hope this helps. 

websearcher

Excellent!  Thank you very much.

Hey! Wasn't this a "Puzzler" on NPR's show "Car Talk" recently?

(websurf, websurf, websurf...)

Yep, it was:

http://www.cartalk.com/content/puzzler/transcripts/200609/index.html
http://www.cartalk.com/content/puzzler/transcripts/200609/answer.html

websearcher- You are really smart!

Actually, the 10th envelope can't have $512 in it -- that would bring
the total of the envelopes to $1023. The largest amount in an envelope
should be $489.

The question doesn't say that the values in the envelope can't add up
beyond 1000, only that you be able to make all values up to 1000. 
Thus, websearcher's answer seems fine to me.  This question is fairly
obvious to anyone with any kind of programming background, but I can
see how it would be tricky otherwise.  It just goes to show that there
are 10 kinds of people in this world: those who understand binary and
those who don't :D

Notes larger than $100 are not in general circulation.