Linear diophantine word problem suggestions

I am looking for a word problem or two that devolves into solving a
linear diophantine equation (i.e., an equation of the form
ax+by = c).

I know one, which I mention below, but I can't seem to find others
that do not rely on tricks (e.g., problems about horses and geese in a
farm that can be solved by 'counting legs' and similar).

The problem I know is:

At a small town, a movie theater charges $5 admission to men, $2 to
women, and 10 cents to children. One afternoon, the owner goes to
check and finds that there are $100 in the box office. When he goes
in, he can count in the darkened theater 100 heads, but cannot tell
how many are men, how many women, and how many children. How many
of each are in the theater?

The problem has a unique solution in positive integers, which can be
found after eliminating one variable from the two obvious equations,
solving the resulting linear diophantine equation, and finding the
only solution where both variables are nonnegative.

You can either post or e-mail me any suggestions you might have by way
of examples or references. Thank you.

--
======================================================================
"It's not denial. I'm just very selective about
what I accept as reality."
--- Calvin ("Calvin and Hobbes")
======================================================================

Arturo Magidin
magidin@xxxxxxxxxxxxxxxxx



.