I have an HP 12C calculator and I'm trying to solve a problem in a
study guide.  The answer the 12C gives in not the same as the one
printed in the study guide.  Doing the problem in Excel returns the
correct result.

Here's the problem:

1/Y = 7; PV = -500; FV = -1,000; CPT -> N = 10.24 years

When I calculate N, I get 11.00.  I had someone else do the same
problem with their 12C and they got 11.00 as well.

If you plug the problem into Excel you get 10.24477.

Here's the Excel formula:

=NPER(7%,0,-500,1000,1)

What I want to know is if there is a way to get the 12C to return the
'correct' answer, and/or why it returns the answer it does.

Brian,
I can only commiserate.  My old HP12c also refuses to give a broken
"n" value, although when I input the 10.24477, it dutifully calculates
6.9xx pa "i".
And, of course, a manual calculation using the "%" key allows the correct result.

Hmm?  Here is an HP12c online handbook, for the Platinum version.  I
did not find it helpful, tried unsuccessfully to consider the problem
as one with 0 cashflows, but didn't master the task.
AH, but I just found on p 49  Sec. 50, that it is explained that it
shows only the next higher "n".

http://h10032.www1.hp.com/ctg/Manual/bpia5184.pdf
 
!! Disappointing, eh?  
I have never needed to, but you can program the HP12c.  If you can
juggle the equation to calculate "n", it should be able to calculate
it correctly.
Good luck, Myoarin

Brian,
The figure of FV would be positive. I got a correct answer with my TI
BAII Plus calculator.
Regards
Daniel