Math Problem Statement
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?
Solution
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:
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Odd-numbered cards: There are five odd-numbered cards , which must always appear in increasing order from left to right in the final arrangement. Therefore, their relative positions are fixed.
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Even-numbered cards: The four even-numbered cards 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:
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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:
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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 (since we can permute the 4 cards):
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Total number of arrangements: The total number of ways to arrange the cards is the product of the two values calculated:
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:
- How does the combination formula work in other contexts?
- Why are the odd-numbered cards fixed in order?
- How would the problem change if the odd-numbered cards could be in any order?
- What would happen if there were more or fewer cards to arrange?
- 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!
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Math Problem Analysis
Mathematical Concepts
Combinatorics
Permutations
Combinations
Formulas
Combination formula: \(\binom{n}{r} = \frac{n!}{r!(n - r)!}\)
Permutation formula: \(n! = n \times (n-1) \times ... \times 1\)
Theorems
Basic principles of permutations and combinations
Suitable Grade Level
Grades 9-12