(ii) 3% of students failed all three courses, 12% failed economics and mathematics, 9% in math and business, and 10% in econ and business. In other words, the students in these groups failed at least the two mentioned courses. Then 12% - 3% = 9% failed only econ and math but not business; 9% - 3% = 6% failed math and business but not econ; and 10% - 3% = 7% failed econ and business but not math. These groups are mutually exclusive, so the total percentage of students that failed exactly two courses is (ii) 9% + 6% + 7% = 22%.
32% failed econ, which means 32% - 12% - 10% + 3% = 13% failed only econ. Similarly, 46% failed business, so 46% - 9% - 10% + 3% = 30% failed only business. But we don't know how many students failed math, so we can't determine how many failed only math... And consequently we can't determine the proportion of students that make up the other categories.
