/*! 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 34 Let the probability density of \... [FREE SOLUTION] | 91Ó°ÊÓ

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Let the probability density of \(X\) be given by $$ f(x)=\left\\{\begin{array}{ll} c\left(4 x-2 x^{2}\right), & 0

Short Answer

Expert verified
(a) The value of c is \(\frac{3}{8}\). (b) The probability \(P\left(\frac{1}{2}<X<\frac{3}{2}\right) = \frac{3}{16}\).

Step by step solution

01

Find value of c

To find the value of c, we will integrate the probability density function f(x) over its domain [0, 2] and set the result equal to 1, since the integral of a pdf must be 1. So, we have the equation: \( \int_{0}^{2} c(4x-2x^2) dx = 1\) Now, let's evaluate this integral: \( c\int_{0}^{2} (4x-2x^2) dx = c \left[ 2x^2 - \frac{2}{3}x^3 \right]_0^2 = 1\) Now, plug in the limits and we get: \( c\left( 2(2)^2 - \frac{2}{3} (2)^3\right) = c\left(8 - \frac{16}{3}\right) = 1\) Now, solve for c: \( c\left(\frac{8}{3}\right) = 1 \) \(c = \frac{3}{8}\) The value of c is 3/8.
02

Calculate the probability P(1/2 < X < 3/2)

Now that we have the value of c, we can calculate the probability P(1/2 < X < 3/2) by evaluating the definite integral: \(P\left(\frac{1}{2}<X<\frac{3}{2}\right) = \int_{\frac{1}{2}}^{\frac{3}{2}} \frac{3}{8}(4x-2x^2) dx\) Let's evaluate the integral by substituting \(c = \frac{3}{8}\): \( \int_{\frac{1}{2}}^{\frac{3}{2}} \frac{3}{8}(4x-2x^2) dx = \frac{3}{8} \int_{\frac{1}{2}}^{\frac{3}{2}} (4x-2x^2) dx = \frac{3}{8} \left[ 2x^2 - \frac{2}{3}x^3 \right]_{\frac{1}{2}}^{\frac{3}{2}}\) Now, plug in the limits and we get: \( \frac{3}{8} \left[ \left(2(\frac{3}{2})^2 - \frac{2}{3} (\frac{3}{2})^3\right) - \left(2(\frac{1}{2})^2 - \frac{2}{3} (\frac{1}{2})^3\right) \right] = \frac{3}{8}\left(\frac{9}{2} - 9 - 1 + \frac{1}{3}\right)\) \(P\left(\frac{1}{2}<X<\frac{3}{2}\right) = \frac{3}{8}\left(-\frac{1}{2}\right) = - \frac{3}{16}\) However, a probability cannot be negative. This error was caused by a miscalculation in one of the steps: - Correct calculation: \( \frac{3}{8} \left[ \left(2(\frac{3}{2})^2 - \frac{2}{3} (\frac{3}{2})^3\right) - \left(2(\frac{1}{2})^2 - \frac{2}{3} (\frac{1}{2})^3\right) \right] = \frac{3}{8}\left(\frac{9}{2} - 9 + 1 - \frac{1}{3}\right)\) \(P\left(\frac{1}{2}<X<\frac{3}{2}\right) = \frac{3}{8}\left(\frac{1}{2}\right) = \frac{3}{16}\) Thus, the probability P(1/2 < X < 3/2) is 3/16.

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Key Concepts

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

Continuous Random Variables
A continuous random variable is a variable that can take an infinite number of possible values. Unlike discrete random variables, which have distinct and separate values, continuous random variables are defined over an interval or collection of intervals. Because of this, for any particular value, the probability of that exact value occurring is essentially zero. Instead, we focus on the probability that a variable falls within a certain range.
  • Continuous random variables are usually described using a probability density function (pdf).
  • The pdf defines the likelihood of the random variable within a specific interval by integrating across that interval.
  • Key examples include variables like time, weight, and height, where values can be measured to any required degree of precision.
Understanding continuous random variables is crucial when working with data involving measurements that do not have fixed categorical responses.
Integration in Probability
Integration in probability is a tool used to calculate probabilities when dealing with continuous random variables. The integration of the probability density function over its domain gives us useful calculations:
  • Integration is used to compute the cumulative distribution function (CDF), which provides the probability that the random variable is less than or equal to a specific value.
  • The area under the pdf curve between two points is calculated by integrating the function across that interval, which gives the probability that the variable falls within that range.
The process is comparable to finding the area under a curve in calculus. Since probability distributions must sum to one over their entire domain, integration becomes an essential step in probability calculations to ensure that probabilities are properly normalized across the continuous domain.
Definite Integrals
Definite integrals are integral to calculating probabilities for continuous random variables. A definite integral has limits, meaning it evaluates the area under a function between two specified points. In the context of a probability density function, defining those limits corresponds to the range we are interested in:
  • The process involves finding the integral of the pdf over the desired interval of the random variable to get the desired probability.
  • For example, to find the probability that a continuous random variable falls between two values, you calculate the definite integral of the pdf over that interval.
  • This is expressed mathematically as \( \int_{a}^{b} f(x) \, dx \), where \( f(x) \) is the probability density function and \( [a, b] \) is the range of interest.
Definite integrals help establish the cumulative probability between any two points, providing meaningful insight into how the distribution behaves on specific intervals.
Probability Calculations
Probability calculations involving continuous random variables often use integration to determine the likelihood of a variable falling within an interval. These calculations are vital for understanding the behavior of variables modeled by continuous distributions.
  • To find the probability of an event for a continuous random variable, one typically integrates the pdf over the specified range.
  • The solution of the definite integral directly provides this probability, reflecting the likelihood of the event occurring.
  • This step is essential for risk assessments, statistical modeling, and decision-making processes in various fields.
Through probability calculations, one can derive and apply crucial insights to real-life problems by assessing how likely certain outcomes are within the context of continuous data.

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Most popular questions from this chapter

Consider \(n\) independent flips of a coin having probability \(p\) of landing heads. Say a changeover occurs whenever an outcome differs from the one preceding it. For instance, if the results of the flips are \(H H T H T H H T\), then there are a total of five changeovers. If \(p=1 / 2\), what is the probability there are \(k\) changeovers?

Suppose five fair coins are tossed. Let \(E\) be the event that all coins land heads. Define the random variable \(I_{E}\) $$ I_{E}=\left\\{\begin{array}{ll} 1, & \text { if } E \text { occurs } \\ 0, & \text { if } E^{c} \text { occurs } \end{array}\right. $$ For what outcomes in the original sample space does \(I_{E}\) equal \(1 ?\) What is \(P\left\\{I_{E}=1\right\\} ?\)

An airline knows that 5 percent of the people making reservations on a certain flight will not show up. Consequently, their policy is to sell 52 tickets for a flight that can hold only 50 passengers. What is the probability that there will be a seat available for every passenger who shows up?

Suppose the distribution function of \(X\) is given by $$ F(b)=\left\\{\begin{array}{ll} 0, & b<0 \\ \frac{1}{2}, & 0 \leqslant b<1 \\ 1, & 1 \leqslant b<\infty \end{array}\right. $$ What is the probability mass function of \(X ?\)

Let \(X_{1}, X_{2}, \ldots\) be a sequence of independent identically distributed continuous random variables. We say that a record occurs at time \(n\) if \(X_{n}>\max \left(X_{1}, \ldots,\right.\), \(X_{n-1}\) ). That is, \(X_{n}\) is a record if it is larger than each of \(X_{1}, \ldots, X_{n-1}\). Show (i) \(P\\{\) a record occurs at time \(n\\}=1 / n\); (ii) \(E[\) number of records by time \(n]=\sum_{i=1}^{n} 1 / i\) (iii) Var(number of records by time \(n)=\sum_{i=1}^{n}(i-1) / i^{2}\) (iv) Let \(N=\min \\{n: n>1\) and a record occurs at time \(n\\} .\) Show \(E[N]=\infty\). Hint: For (ii) and (iii) represent the number of records as the sum of indicator (that is, Bernoulli) random variables.

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