Math Problem Statement

  1. On a test in a math class there are 8 questions, and you must answer 5 of them.
  2. How many ways can you choose the 5 questions if the order does not matter?
  3. How many ways can you choose the 5 questions if the order does matter?

Solution

Let's break down both parts of this problem:

1. How many ways can you choose 5 questions if the order does not matter?

When the order doesn't matter, this is a combination problem. The formula for combinations is:

C(n,k)=n!k!(nk)!C(n, k) = \frac{n!}{k!(n-k)!}

Where:

  • nn is the total number of items (in this case, 8 questions),
  • kk is the number of items you want to choose (in this case, 5 questions).

Thus, we need to calculate:

C(8,5)=8!5!(85)!=8!5!3!C(8, 5) = \frac{8!}{5!(8-5)!} = \frac{8!}{5!3!}

Now, calculate this:

C(8,5)=8×7×63×2×1=56C(8, 5) = \frac{8 \times 7 \times 6}{3 \times 2 \times 1} = 56

So, there are 56 ways to choose 5 questions when the order does not matter.

2. How many ways can you choose the 5 questions if the order does matter?

When the order does matter, this is a permutation problem. The formula for permutations is:

P(n,k)=n!(nk)!P(n, k) = \frac{n!}{(n-k)!}

Where:

  • nn is the total number of items (8 questions),
  • kk is the number of items you want to choose (5 questions).

Thus, we need to calculate:

P(8,5)=8!(85)!=8!3!P(8, 5) = \frac{8!}{(8-5)!} = \frac{8!}{3!}

Now, calculate this:

P(8,5)=8×7×6×5×41=6720P(8, 5) = \frac{8 \times 7 \times 6 \times 5 \times 4}{1} = 6720

So, there are 6720 ways to choose and arrange 5 questions when the order does matter.


Summary:

  1. 56 ways to choose 5 questions when order does not matter (combination).
  2. 6720 ways to choose 5 questions when order does matter (permutation).

Would you like more details on the formulas used or any further questions on combinations and permutations? Here are some related topics to explore:

  1. What are the differences between combinations and permutations?
  2. How do you calculate combinations when there are repeated elements?
  3. How can you solve permutation problems when there are restrictions on the order?
  4. What is the general rule for counting in combinatorics (e.g., multiplication principle)?
  5. How does the factorial function relate to both combinations and permutations?

Tip: When solving combinatorics problems, carefully determine whether order matters (permutation) or does not matter (combination), as the formula changes!

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Math Problem Analysis

Mathematical Concepts

Combinatorics
Permutations
Combinations

Formulas

C(n, k) = n! / (k!(n-k)!)
P(n, k) = n! / (n-k)!

Theorems

Combination Theorem
Permutation Theorem

Suitable Grade Level

Grades 8-10

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