Maxima of discrete functions involving nPr, nCr, etc?

In summary, the formula for finding the maximum value of a discrete function involving nPr is nPr = n!/(n-r)!, where n is the total number of items and r is the number of items being selected. This maximum value can never be negative and changes as n and r vary, increasing with n and decreasing with r. There is a relationship between nPr and nCr, and real-world applications include probability calculations, statistics, and various fields of study such as computer science and economics.
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Homework Statement



So I want to prove that the expression 20Cr×0.1r 0.9(20-r) reaches maximum value for r=(0.1)×20=2

Homework Equations

The Attempt at a Solution


I can prove it by trial and error but can't differentiate the expression because nCr isn't continuous.
 
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FAQ: Maxima of discrete functions involving nPr, nCr, etc?

1. What is the formula for calculating the maximum value of a discrete function involving nPr?

The formula for finding the maximum value of a discrete function involving nPr is nPr = n!/(n-r)!, where n is the total number of items and r is the number of items being selected.

2. Can the maximum value of a discrete function involving nPr ever be negative?

No, the maximum value of a discrete function involving nPr can never be negative. This is because nPr represents the number of ways to choose r items from a total of n items, and negative values do not make sense in this context.

3. How does the maximum value of a discrete function involving nPr change as n and r vary?

The maximum value of a discrete function involving nPr increases as n increases and decreases as r increases. This is because as the total number of items (n) increases, there are more ways to choose r items, resulting in a larger maximum value. Similarly, as the number of items being selected (r) increases, there are fewer ways to choose r items, resulting in a smaller maximum value.

4. Is there a relationship between the maximum value of a discrete function involving nPr and nCr?

Yes, there is a relationship between the maximum value of a discrete function involving nPr and nCr. Specifically, nPr = nCr * r!, where n is the total number of items, r is the number of items being selected, and r! represents the factorial of r. This relationship holds true because nPr represents the number of ways to choose r items from a total of n items, which is the same as nCr multiplied by the number of ways to arrange those r items (r!).

5. Are there any real-world applications of finding the maximum value of a discrete function involving nPr?

Yes, there are many real-world applications of finding the maximum value of a discrete function involving nPr. For example, it can be used in probability calculations to determine the likelihood of selecting a certain combination of items from a larger set. It is also commonly used in statistics and data analysis to determine the maximum possible outcomes of a given scenario. Additionally, it has applications in fields such as computer science, engineering, and economics.

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