Some people already know about this, but not everybody:
By way of background: IMHO multiple-guess questions are an
abomination. Students should be allowed to write more-or-less
free-form answers, for about a dozen reasons.
Now suppose the correct answer is ½ sin 2θ, and some student
comes up with the answer sin(θ) cos(θ). Are you going to mark
it wrong?
Or suppose the correct answer is 1/√(1-x ^ 2), and some student
comes up with the answer cosh(asinh(x)). Are you going to mark
that it wrong?
With some thought you can figure out that each pair of answers
is equivalent, but if you're teaching a huge class you haven't
got time to put much thought into grading the quizzes.
It turns out that you can automate the process. There are two
different moodle plugins that will do it for you. You type
in your answer, the students type in their answers, and the
machine does the comparison.
Neither of these is a built-in feature of basic moodle, but
they are readily installable plugins.
a) The light-weight plugin is what I call the "golf cart". It
is ridiculously easy to install, if you already have a working
moodle system. It contains its own simple machinery for parsing
and evaluating expressions. https://www.av8n.com/cgit/moodle-qtype_algebra/about/
If all you need to do is run to the corner store for a few
groceries, the golf cart is more practical.
For a family cross-country trip, neither the golf cart nor
the 1000 hp dump truck is practical.
I suspect the STACK system is the way of the future. It is under
active development. The hope is that there will eventually be a
big library of ready-made questions you can draw from, and some
decent documentation, but we're not there yet.
The guy who was maintaining the light-weight "algebra" plugin
retired a couple of years ago. Since then I have fixed a few
bugs and implemented a few creeping features. It's probably not
worth putting too much development effort into this, because I
reckon it's not the way of the future ... but it's quite usable
as-is.