8P4 11C7

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
Problem 1RQ
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The expression in the image is a fraction involving permutations and combinations. It is written as:

\[
\frac{{^8P_4}}{{^{11}C_7}}
\]

### Explanation:

1. **Permutations (\(^nP_r\))**:
   - \(^8P_4\) represents the number of ways to arrange 4 items out of 8 distinct items where the order matters. It is calculated using the formula:
     \[
     ^nP_r = \frac{n!}{(n-r)!}
     \]
     So, \(^8P_4 = \frac{8!}{(8-4)!} = \frac{8!}{4!}\).

2. **Combinations (\(^nC_r\))**:
   - \(^1C_7\) represents the number of ways to choose 7 items from 11 distinct items where the order does not matter. It is calculated using the formula:
     \[
     ^nC_r = \frac{n!}{r!(n-r)!}
     \]
     So, \(^1C_7 = \frac{11!}{7! \cdot (11-7)!} = \frac{11!}{7! \cdot 4!}\).

This fraction represents the ratio of the number of permutations of 8 items taken 4 at a time to the number of combinations of 11 items taken 7 at a time.
Transcribed Image Text:The expression in the image is a fraction involving permutations and combinations. It is written as: \[ \frac{{^8P_4}}{{^{11}C_7}} \] ### Explanation: 1. **Permutations (\(^nP_r\))**: - \(^8P_4\) represents the number of ways to arrange 4 items out of 8 distinct items where the order matters. It is calculated using the formula: \[ ^nP_r = \frac{n!}{(n-r)!} \] So, \(^8P_4 = \frac{8!}{(8-4)!} = \frac{8!}{4!}\). 2. **Combinations (\(^nC_r\))**: - \(^1C_7\) represents the number of ways to choose 7 items from 11 distinct items where the order does not matter. It is calculated using the formula: \[ ^nC_r = \frac{n!}{r!(n-r)!} \] So, \(^1C_7 = \frac{11!}{7! \cdot (11-7)!} = \frac{11!}{7! \cdot 4!}\). This fraction represents the ratio of the number of permutations of 8 items taken 4 at a time to the number of combinations of 11 items taken 7 at a time.
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