Math Problem Statement

If the random variable X takes the values 1, 2, 3, and 4 such that 2P(X = 1) = 3P(X = 2) = P(X = 3) = 5P(X = 4), find the probability distribution and the cumulative distribution function of X.

Solution

Let XX be a discrete random variable taking values 1,2,3,41, 2, 3, 4, and the relationships provided are:

2P(X=1)=3P(X=2)=P(X=3)=5P(X=4)2P(X = 1) = 3P(X = 2) = P(X = 3) = 5P(X = 4)

Let the probabilities of these events be expressed in terms of a common variable. Let:

P(X=4)=pP(X = 4) = p

Using the given relations, we can express the other probabilities in terms of pp:

P(X=3)=5pP(X = 3) = 5p P(X=2)=5p3P(X = 2) = \frac{5p}{3} P(X=1)=5p6P(X = 1) = \frac{5p}{6}

Now, since the total probability must sum to 1 (i.e., P(X=1)+P(X=2)+P(X=3)+P(X=4)=1P(X = 1) + P(X = 2) + P(X = 3) + P(X = 4) = 1), we have:

5p6+5p3+5p+p=1\frac{5p}{6} + \frac{5p}{3} + 5p + p = 1

We can now solve for pp. First, let's get a common denominator for the terms on the left-hand side:

5p6+10p6+30p6+6p6=1\frac{5p}{6} + \frac{10p}{6} + \frac{30p}{6} + \frac{6p}{6} = 1

Simplifying the left-hand side:

51p6=1\frac{51p}{6} = 1

Solving for pp:

p=651=217p = \frac{6}{51} = \frac{2}{17}

Now we can find the probabilities:

P(X=4)=217,P(X=3)=5p=1017,P(X=2)=5p3=1051=1017,P(X=1)=5p6=517P(X = 4) = \frac{2}{17}, \quad P(X = 3) = 5p = \frac{10}{17}, \quad P(X = 2) = \frac{5p}{3} = \frac{10}{51} = \frac{10}{17}, \quad P(X = 1) = \frac{5p}{6} = \frac{5}{17}

Probability Distribution:

  • P(X=1)=517P(X = 1) = \frac{5}{17}
  • P(X=2)=1051P(X = 2) = \frac{10}{51}
  • P(X=3)=1017P(X = 3) = \frac{10}{17}
  • P(X=4)=217P(X = 4) = \frac{2}{17}

Cumulative Distribution Function (CDF):

To find the cumulative distribution function F(X)F(X), we sum the probabilities up to each value of XX:

  • F(1)=P(X=1)=517F(1) = P(X = 1) = \frac{5}{17}
  • F(2)=P(X=1)+P(X=2)=517+1017=1071F(2) = P(X = 1) + P(X = 2) = \frac{5}{17} + \frac{10}{17} = \frac{10}{71}

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Math Problem Analysis

Mathematical Concepts

Probability
Discrete Probability Distributions

Formulas

2P(X = 1) = 3P(X = 2) = P(X = 3) = 5P(X = 4)
Sum of probabilities: P(X = 1) + P(X = 2) + P(X = 3) + P(X = 4) = 1

Theorems

Law of Total Probability

Suitable Grade Level

Undergraduate (Probability Theory)