Consider a collection of cards numbered from 1 to 9. 1 23 4 5 6 789 All nine cards are arranged in a row so that if the numbers are read from left to right, the odd numbers are in increasing order. The even-numbered cards can be in any order. An example is shown below. 1 8 4 3 5 7 26 9 (a) How many ways can this be done?

We are given a collection of cards numbered from 1 to 9. The odd-numbered cards (1, 3, 5, 7, 9) must be placed in increasing order from left to right, while the even-numbered cards (2, 4, 6, 8) can be arranged in any order. 

### Problem Breakdown:

1. **Odd-numbered cards**: There are five odd-numbered cards \(\{1, 3, 5, 7, 9\}\), which must always appear in increasing order from left to right in the final arrangement. Therefore, their relative positions are fixed.

2. **Even-numbered cards**: The four even-numbered cards \(\{2, 4, 6, 8\}\) can be placed in any order. So, we need to determine how many ways we can assign these four cards to the remaining four positions.

### Step-by-Step Solution:

1. **Choose 4 positions for the even cards**: There are 9 total positions, and we need to choose 4 positions for the even-numbered cards. The number of ways to do this is given by the combination formula:
   \[
   \binom{9}{4} = \frac{9 \times 8 \times 7 \times 6}{4 \times 3 \times 2 \times 1} = 126
   \]

2. **Arrange the even cards in the chosen positions**: Once the positions are chosen, the 4 even-numbered cards can be arranged in any order in these positions. The number of ways to arrange the 4 even-numbered cards is \(4!\) (since we can permute the 4 cards):
   \[
   4! = 4 \times 3 \times 2 \times 1 = 24
   \]

3. **Total number of arrangements**: The total number of ways to arrange the cards is the product of the two values calculated:
   \[
   \text{Total ways} = \binom{9}{4} \times 4! = 126 \times 24 = 3024
   \]

Thus, the total number of ways to arrange the cards such that the odd-numbered cards are in increasing order is **3024**.

---

Would you like to explore any part of this solution in more detail or ask questions?

Here are 5 related questions you might find helpful:
1. How does the combination formula \(\binom{9}{4}\) work in other contexts?
2. Why are the odd-numbered cards fixed in order?
3. How would the problem change if the odd-numbered cards could be in any order?
4. What would happen if there were more or fewer cards to arrange?
5. How does this problem connect to the concept of permutations?

**Tip**: When dealing with both combinations and permutations in a problem, make sure to distinguish when order matters and when it doesn’t!

Learn how to arrange a collection of cards numbered from 1 to 9 such that odd numbers are in increasing order while even numbers can be in any order. This solution uses key combinatorics concepts including combinations and permutations, suitable for students in Grades 9-12.

Math Problem Statement

Solution

Ask a new question for Free

By Image

Math Problem Analysis

Mathematical Concepts

Formulas

Theorems

Suitable Grade Level

Related Recommendation