Random variables - Exercise set 1

This exercise set contains some solved exercises on discrete random variables and probability mass functions. The theory needed to solve these exercises is introduced in the lecture entitled Random variables.

Exercise 1.1

Let X be a discrete random variable. Let its support R_X be:[eq1]

Let its probability mass function [eq2] be:[eq3]

Calculate the following probability:[eq4]

nav_button Solution

Using the additivity of probability:[eq5]

Exercise 1.2

Let X be a discrete random variable. Let its support R_X be the set of the first $20$ natural numbers:[eq6]

Let its probability mass function [eq2] be:[eq8]

Compute the probability:[eq9]

nav_button Solution

By the additivity of probability:[eq10]

Exercise 1.3

Let X be a discrete random variable. Let its support R_X be:[eq11]

Let its probability mass function [eq2] be:[eq13]where [eq14] is the binomial coefficient.

Calculate the probability:[eq15]

nav_button Solution

First note that, by additivity:[eq16]

Therefore, in order to compute [eq17], we need to evaluate the probability mass function at the three points $x=0\,$, $x=1$ and $x=2$:[eq18]

Finally:[eq19]

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