I want to create a multiple choice questions with four options, in which multiple answers are allowed. Full marks for the question should be 4. I want to use following rules to grade the question
1. Full Marks : +4 If only (all) the correct option(s) is(are) chosen;
2. Partial Marks : +3 If all the four options are correct but ONLY three options are chosen;
3. Partial Marks : +2 If three or more options are correct but ONLY two options are chosen, both of which are correct;
4. Partial Marks : +1 If two or more options are correct but ONLY one option is chosen and it is a correct option;
5. Zero Marks : 0 If none of the options is chosen (i.e. the question is unanswered);
6. Negative Marks : -1 In all other cases.
I first thought I would just divide the 100% equally among all the options which are correct, but I can't figure out how do I implement my 6th rule, so that even if one of the wrong options are selected, the total marks becomes -1, disregarding what other options have been selected. Please help.