7) Suppose that a class of 20 students is assigned to write an essay. Suppose 4 essays are picked at random. How many groups of 4 are possible? What if the 4 essays picked at random are given awards of $35, $20, $10, and $5. How many groups of 4 are possible now?

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---

**Suppose that a class of 20 students is assigned to write an essay.**

**Question:**
1. **Suppose 4 essays are picked at random.**
   - How many groups of 4 are possible?

2. **What if the 4 essays picked at random are given awards of $35, $20, $10, and $5?**
   - How many groups of 4 are possible now?

In this scenario, we want to explore two different types of combinations:
- **Combination without regard to order (unlabeled):** This is the case in which essays are selected purely based on the group, without any distinction between them.
- **Combination with regard to order (labeled):** This is the case where each essay picked is assigned a specific award, implying that the order of selection now matters.

---

### Explanation of Concepts:

1. **Unordered Combinations (Unlabeled):**
   - This refers to selecting 4 essays from the 20 in the class without considering any order of selection.
   - To calculate this, we use the combination formula \(\binom{n}{k}\), where \(n\) is the total number of items to choose from, and \(k\) is the number of items to choose.
   - Formula: \(\binom{20}{4} = \frac{20!}{4!(20-4)!}\)

2. **Ordered Combinations (Labeled):**
   - When the 4 essays are awarded specific amounts of money ($35, $20, $10, and $5), the order in which the essays are chosen now matters.
   - This is a factorial problem represented by \(n!\), where each position is distinct.
   - Formula: \(P(20, 4) = 20!/(20-4)!\)

### Calculation Illustrations:

- **Unordered Combinations:**
  \[
  \binom{20}{4} = \frac{20!}{4!(20-4)!} =  \frac{20!}{4! \cdot 16!} =  \frac{20 \times 19 \times 18 \times 17}{4 \times 3 \times 2 \times 1} = 4845
  \]
  Therefore, 4,845 different groups of
Transcribed Image Text:Certainly! Here's the transcription suitable for an educational website: --- **Suppose that a class of 20 students is assigned to write an essay.** **Question:** 1. **Suppose 4 essays are picked at random.** - How many groups of 4 are possible? 2. **What if the 4 essays picked at random are given awards of $35, $20, $10, and $5?** - How many groups of 4 are possible now? In this scenario, we want to explore two different types of combinations: - **Combination without regard to order (unlabeled):** This is the case in which essays are selected purely based on the group, without any distinction between them. - **Combination with regard to order (labeled):** This is the case where each essay picked is assigned a specific award, implying that the order of selection now matters. --- ### Explanation of Concepts: 1. **Unordered Combinations (Unlabeled):** - This refers to selecting 4 essays from the 20 in the class without considering any order of selection. - To calculate this, we use the combination formula \(\binom{n}{k}\), where \(n\) is the total number of items to choose from, and \(k\) is the number of items to choose. - Formula: \(\binom{20}{4} = \frac{20!}{4!(20-4)!}\) 2. **Ordered Combinations (Labeled):** - When the 4 essays are awarded specific amounts of money ($35, $20, $10, and $5), the order in which the essays are chosen now matters. - This is a factorial problem represented by \(n!\), where each position is distinct. - Formula: \(P(20, 4) = 20!/(20-4)!\) ### Calculation Illustrations: - **Unordered Combinations:** \[ \binom{20}{4} = \frac{20!}{4!(20-4)!} = \frac{20!}{4! \cdot 16!} = \frac{20 \times 19 \times 18 \times 17}{4 \times 3 \times 2 \times 1} = 4845 \] Therefore, 4,845 different groups of
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