A student has to opt for 2 subjects out of 5 subjects for a course. Namely commerce, economics, statistics, mathematics 1 and Mathematics 2, Mathematics 2 can be offered only if mathematics 1 has also opted. The number of different combinations of two subjects which can be opted is_________?
Correct answer: C. 7
- A. 5
- B. 6
- C. 7
- D. 18
Explanation
There are 5C2 = 10 unrestricted pairs of subjects. The three invalid pairs are Mathematics 2 with commerce, economics or statistics, because Mathematics 1 is missing, so 10 - 3 = 7 valid combinations; 6 usually results from also wrongly excluding the pair Mathematics 1 and Mathematics 2.
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