/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 73 In Section 3.6.3, we saw that if... [FREE SOLUTION] | 91Ó°ÊÓ

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In Section 3.6.3, we saw that if \(U\) is a random variable that is uniform on \((0,1)\) and if, conditional on \(U=p, X\) is binomial with parameters \(n\) and \(p\), then $$ P[X=t\\}=\frac{1}{n+1}, \quad i=0,1, \ldots, n $$ For another way of showing this result, let \(U, X_{1}, X_{2}, \ldots, X_{n}\) be independent uniform \((0,1)\) random variables. Define \(X\) by $$ \boldsymbol{X}=\boldsymbol{h i}: \boldsymbol{X}_{i}<\boldsymbol{U} $$ That is, if the \(n+1\) variables are ordered from smallest to largest, then \(U\) would be in position \(X+1\). (a) What is \(P[X=i] ?\) (b) Explain how this proves the result stated in the preceding.

Short Answer

Expert verified
We found the probability of \(X=i\) using uniform random variables \(X_1, X_2, \ldots, X_n\) as: $$P[X = i] = \frac{1}{n+1}$$ which agrees with the given result that states: $$P[X=t]=\frac{1}{n+1}, \quad i=0,1, \ldots, n$$ This validates the given result using an alternative method and proves it as true.

Step by step solution

01

Define the event that X = i

For X = i, U is larger than X_1, X_2, ..., X_i, but smaller than X_(i+1), X_(i+2), ..., X_n. We want to find the probability of this event happening.
02

Calculate the probability of X = i

Now, we will use the fact that the random variables are uniformly distributed in the range (0, 1). So, the probability of U being greater than X_i for i = 1, 2, ...k, and U less than X_i for i = k+1, k+2, ...n can be written as the probability of arranging n+1 variables in a specific order. The probability can be calculated as the number of favorable arrangements divided by the total number of possible arrangements. There are (n+1)! total arrangements and (i)!(n-i)! favorable arrangements. Hence, $$P[X = i] = \frac{(i)!(n-i)!}{(n+1)!}$$
03

Simplify the expression

The expression can be simplified by dividing the numerator and denominator by i!(n-i)!: $$P[X = i] = \frac{1}{n+1}$$
04

Relate this result to the given result

We have found that the probability of X = i is equal to \(\frac{1}{n+1}\) using an alternative method. This result agrees with the given result, that states: $$P[X=t]=\frac{1}{n+1}, \quad i=0,1, \ldots, n$$ Hence, our calculations and findings prove the given result.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Uniform Distribution
A uniform distribution in probability theory is a type of continuous distribution where every outcome in a particular range has an equal chance of occurring. Imagine picking a random number from 0 to 1. Under uniform distribution, every number has an equal chance of being picked.

For the example in the exercise, the random variable \( U \) is uniformly distributed over the interval (0, 1). This means that no particular value within that range is more likely to be chosen over any other. This concept is useful when calculating probabilities because it simplifies the problem: each number is equally probable, so calculations about arrangements or orderings become more straightforward.

In order problems, whenever you encounter uniform distribution, remember it's like having a fair game where no individual outcome is preferred. This makes for a balanced scenario crucial for certain statistical proofs like the one given.
Binomial Distribution
The binomial distribution is another cornerstone of probability theory. It is a discrete distribution that captures the number of successes in a fixed number of independent trials of a binary experiment. Think of it like flipping a coin, where each flip (trial) can result in heads (success) or tails (failure).

In this exercise, suppose we define a random variable \( X \) which represents the number of times a specific event occurs in \( n \) trials with a success probability \( p \). If we set \( p \) as the outcome of the uniform random variable \( U \), the conditional distribution of \( X \) given \( U \) becomes binomial as specified by parameters \( n \) and \( p \).

The elegance of the binomial distribution is its simplicity and relevance in real-world applications, helping us predict the likelihood of a certain number of successes given a specific probability of those successes happening.
Random Variables
In probability and statistics, a random variable is a quantitative representation of an outcome from a probabilistic event or experiment. It’s a way of associating a numerical value to each possible outcome; this helps in analyzing and predicting outcomes based on probability concepts.

The exercise defines \( U \) and \( X \) as random variables. Here, \( U \) comes from a uniform distribution (between 0 and 1), and \( X \) is defined using the results of the uniform variables \( X_i \). This showcases not only the nature of random variables but how they can be related or conditioned upon each other to evaluate probabilities.

Random variables are crucial in describing and analyzing stochastic processes, further helping in making informed predictions based on collected or assumed data.
Stochastic Processes
Stochastic processes, in simple terms, are processes that involve a sequence or series of random variables. They represent systems or models that evolve over time in a random manner. These processes are fundamental in fields such as finance, telecommunications, and engineering, modeling phenomena ranging from stock prices to the movement of particles.

In the context of the exercise, combining the uniform distribution of \( U \) and the conditional binomial distribution of \( X \) forms a simple stochastic process. Each step, such as the drawing of \( n+1 \) independent uniform variables, contributes to understanding how \( X \) behaves.

Recognizing the structure of stochastic processes helps in critically assessing and interpreting complex models where randomness plays an integral role in the system's evolution.

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Most popular questions from this chapter

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