Math Problem Statement

A variável aleatória discreta X assume os seguintes valores: -13, -10, -9, -5, 2, 10 com as seguintes probabilidades, respectivamente: 1/49, 13/49, 9/49, 10/49, 11/49, 5/49. Encontre a variância de X.

Solution

To find the variance of the discrete random variable XX, we will follow these steps:

  1. List of values and probabilities:

    • X=13,10,9,5,2,10X = -13, -10, -9, -5, 2, 10
    • Corresponding probabilities: P(X=13)=149,P(X=10)=1349,P(X=9)=949,P(X=5)=1049,P(X=2)=1149,P(X=10)=549P(X = -13) = \frac{1}{49}, P(X = -10) = \frac{13}{49}, P(X = -9) = \frac{9}{49}, P(X = -5) = \frac{10}{49}, P(X = 2) = \frac{11}{49}, P(X = 10) = \frac{5}{49}
  2. Compute the expected value E[X]\mathbb{E}[X]: E[X]=ixiP(xi)=(13)149+(10)1349+(9)949+(5)1049+21149+10549\mathbb{E}[X] = \sum_i x_i P(x_i) = (-13)\frac{1}{49} + (-10)\frac{13}{49} + (-9)\frac{9}{49} + (-5)\frac{10}{49} + 2\frac{11}{49} + 10\frac{5}{49}

  3. Compute the expected value of X2X^2 (i.e., E[X2]\mathbb{E}[X^2]): E[X2]=ixi2P(xi)=(13)2149+(10)21349+(9)2949+(5)21049+221149+102549\mathbb{E}[X^2] = \sum_i x_i^2 P(x_i) = (-13)^2\frac{1}{49} + (-10)^2\frac{13}{49} + (-9)^2\frac{9}{49} + (-5)^2\frac{10}{49} + 2^2\frac{11}{49} + 10^2\frac{5}{49}

  4. Find the variance Var(X)\text{Var}(X): [ \text{Var}(X) = \mathbb{E}[X^2] - (\mathbb{E}[X])^2 ]

Let me calculate each step.Here are the results for the discrete random variable XX:

  1. Expected value E[X]\mathbb{E}[X]: E[X]=4.1224\mathbb{E}[X] = -4.1224

  2. Expected value of X2X^2, i.e., E[X2]\mathbb{E}[X^2]: E[X2]=61.0612\mathbb{E}[X^2] = 61.0612

  3. Variance of XX, i.e., Var(X)\text{Var}(X): Var(X)=44.0666\text{Var}(X) = 44.0666

If you have any questions or would like more details, feel free to ask!


Here are 5 related questions:

  1. How would the variance change if we adjusted the probabilities?
  2. What is the significance of a negative expected value?
  3. How is variance affected if the data points are further spread out?
  4. How does the expected value of X2X^2 contribute to calculating variance?
  5. Can you derive the standard deviation from the variance?

Tip: The standard deviation is the square root of the variance, giving a measure of spread in the same units as the data itself.

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Math Problem Analysis

Mathematical Concepts

Probability
Statistics
Variance
Expected Value

Formulas

Expected Value: E(X) = Σ x_i * P(x_i)
Variance: Var(X) = E(X^2) - [E(X)]^2

Theorems

Law of Total Expectation
Variance Definition for Discrete Random Variables

Suitable Grade Level

University level - Probability and Statistics