Ch 2 · Permutations and Combinations

⭐ Important points (exam-critical)

• ⭐When repetition allowed: arrangements of r items from n = nʳ.
• ⭐Identical items in arrangement: divide by factorial of identicals (n!/p!q!).
• ⭐Selection of at least 1: 2ⁿ − 1.
• ⭐Distinguish 'word formation' MCQs — vowels together / never together patterns.