Step 1: Understanding the Concept:
This problem uses the Fundamental Principle of Counting, specifically the Product Rule. When one event can occur in $m$ ways and a second event can occur in $n$ ways, the number of ways the two events can occur together is $m \times n$. Step 2: Key Formula or Approach:
Total ways = (Number of Shirt options) $\times$ (Number of Trouser options) Step 3: Detailed Explanation:
1. Ram must choose one shirt AND one trouser to complete an outfit.
2. Number of ways to choose a shirt = 4.
3. Number of ways to choose a trouser = 5.
4. Total combinations = $4 \times 5 = 20$. Step 4: Final Answer:
Ram can choose his outfit in 20 ways.