Permutations: Arranging Part of a Set

🔑 Key Concepts

  • A permutation is an arrangement where order matters.
  • The notation \( nPr \) means arranging \( r \) items from \( n \) total items.
  • The formula is \( nPr=\frac{n!}{(n-r)!} \).
  • The shortcut is to multiply the first \( r \) factors of \( n! \).

💡 Main Idea

Permutations are used when arranging items and the order matters. For example, choosing the first, second, and third hitters in a lineup is different from choosing the same players in a different order.

✏️ Worked Example

🧠 Math Vocabulary

  • Permutation: An arrangement of items where order matters.
  • Arrangement: A specific order or placement of items.
  • nPr: A notation for arranging \( r \) items from \( n \) total items.
  • Factorial: The product of a number and all positive whole numbers below it, such as \( 5! = 5 \times 4 \times 3 \times 2 \times 1 \).
  • n: The total number of items available.
  • r: The number of items being arranged.
  • Order Matters: Changing the order creates a different outcome.

📚 What You Should Already Know

Students should know how to multiply whole numbers, understand factorial notation, and recognize whether a counting situation depends on order.

🚀 What Comes Next

Next, students can compare permutations with combinations, where order does not matter, and use both strategies in probability and counting problems.

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