Factorial Notation, NPr And NCr
Overview
Once you know whether order matters, you need fast formulas to do the counting. Factorial notation packs a long product into a single symbol, and from it come the two workhorse formulas of counting: \(^nP_r\) for permutations and \(^nC_r\) for combinations. With these you can count arrangements and selections in one step.
In this lesson you will learn what \(n!\) means, the surprising but essential fact that \(0!=1\), and how to use the permutation and combination formulas confidently. Worked examples like \(^5P_2=20\) and \(^5C_2=10\) show the formulas in action.
Objectives
- Know and use the notation n! (with 0! = 1) and the expressions for permutations and combinations of n items taken r at a time.
- Solve problems on arrangement and selection using permutations or combinations.
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Lesson Evaluation
Congratulations on completing the lesson on Factorial Notation, NPr And NCr. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- What is the value of 5!? A. 25 B. 60 C. 120 D. 720 Answer: C
- What is the value of 0!? A. 0 B. 1 C. undefined D. infinity Answer: B
- Evaluate 5P2. A. 10 B. 15 C. 20 D. 25 Answer: C
- Evaluate 5C2. A. 10 B. 15 C. 20 D. 25 Answer: A
- Which formula gives the number of combinations of r from n? A. n!/(n - r)! B. n!/(r!(n - r)!) C. n! r! D. n!/r! Answer: B
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