I am having an issue with this situation with a question were student must choose "all that apply": A multiple choice question with 4 options, 2 of which are required to get the full points (allow multiple answers set to yes). So what I do is set each of the correct answers at 50%, this means that they both must be given to get 100% of the points. I cannot figure out how to get Moodle to take away credit if one of the 2 wrong answers is chosen. At first, I set each wrong answer as minus 50%. That didn't work out well here is what happened: A student chose 1 correct and 1 incorrect answer. 0/1 Marks (the 50% and -50% canceled each other out). The student should have gotten a 50% on the question. I went back and took out the -50% for both wrong answers which still didn't work because then another student simply chose all 4 answers and got full credit because they checked the two right ones, but there was no penalty for choosing the wrong ones as well. Then I tried setting it for minus 25% for each wrong answer, but once again, a student who got one right and one wrong, should have gotten a 50% only got a 25%.
The only conclusion I can come to is that Moodle can't deal with what I am wanting and I just need to say "Choose ONE of the correct answers" and not "Choose all that apply".
EDIT: Here is a thing NOT to do. I went back and rewrote the question to state that they only needed to give me ONE of the correct answers. I set it to "only one correct answer" and did a regrade. I wanted to go ahead and give full credit to anyone what had chosen at least one of the two correct answers. Apparently when you change a multiple choice question from "multiple answers" to "just one answer" it completely wipes all responce data that contains two choices. Only those that selected one answer to begin with kept their grade, the rest: no answers given.