A students has to opt for 2 subjects out of 5 subjects for a course, namely, Commerce, Economics, Statistics, Mathematics I and Mathematics II. Mathematics II can be offered only if Mathematics I is also opted. The number of different combinations of two subjects which can be opted is
Explanation:
Problem Analysis
A student has to select 2 subjects out of 5 available subjects: Commerce (C), Economics (E), Statistics (S), Mathematics I (M1), and Mathematics II (M2). However, there is a restriction:
– Mathematics II (M2) can only be selected if Mathematics I (M1)ย is also selected.
We need to calculate the number of valid combinations of 2 subjects under this condition.
Step 1: List all possible combinations
Without the restriction, the total number of combinations of 2 subjects from 5 is:
$$
\binom{5}{2} = \frac{5 \cdot 4}{2} = 10.
$$
However, the restriction eliminates certain combinations. Specifically:
– M2 cannot be selected without M1, meaning any combination involving M2 but not M1ย is invalid.
Step 2: Identify valid combinations
Let us evaluate the valid combinations manually:
1. Combinations not involving M2:
These are all combinations of the remaining 4 subjects (C, E, S, and M1):
$$
\{C, E\}, \{C, S\}, \{C, M1\}, \{E, S\}, \{E, M1\}, \{S, M1\}.
$$
There are 6 such combinations.
2. Combinations involving M2:
Since M2 can only be chosen if M1 is also chosen, the only valid combinations with M2 are:
$$
\{M1, M2\}.
$$
There is 1 such combination.
Step 3: Total valid combinations
Adding these:
$$
\text{Total valid combinations} = 6 + 1 = 7.
$$
Final Answer:
The number of valid combinations is:
$$
\boxed{\text{(c) 7}}
$$