Showing posts with label Binomial. Show all posts
Showing posts with label Binomial. Show all posts

Friday, August 24

Binomial Random Variable

Introduction to binomial random variable:

Binomial Random variables help us to make a link between probability and numbers that we observe as data.

Binomial Random Variable: A numerical valued function defined on a sample space. A random variable X “maps” an outcome in a sample space to a numerical value. We use capital letters such as X or Y to denote binomial random variables. Let s be an elementary outcome. A value, X(s), of X is denoted x.

A binomial random variable is discrete if it can take on a finite or countable number of values. A continuous random variable takes on an uncountable number of values.

Binomial Random Variable:

General features of a Binomial Random Variable:

The binomial random experiment consists of n identical trials.
Possible outcomes on each trial are of only two. given one outcome by S (for Success) and the other by F (for Failure).

The probability for Success(S) remains the same from trial to trial. Denote it by p=Pr(Success).

The trials of binomial random experiment are independent of each other.

Then we say  Binomial Random Variable X as the number of Successes in n trials.

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Binomial Random Variable:

Ex 1:  What is the probability we roll less than a 5?

Sol :              P(X < 5) = P(X = 2) + P(X = 3) + P(X = 4)

                              = 1/36 + 2/36 + 3/36

                              = 6/36

                  the probability we roll less than a 5  = 1/6

Ex 2 :  What is the probability we roll a number between 7 and 10  (inclusive)?

Sol :                              P(7 `<=` X `<=` 10) = P(X = 7) + P(X = 8) + .......

                                       = 6/36 + 5/36 + 4/36 + 3/36

                                       = 18/36

         the probability we roll a number between 7 and 10 (inclusive) = 1/2

Ex 3 :  What is the probability the sum of two dice will be odd?

Sol :              P(X odd) = P(X = 3) + P(X = 5) + ..........

                     = 2/36 + 4/36 + 6/36 + 4/36 + 2/36

                     = 18/36

              the probability the sum of two dice will be odd = 1/2

Ex 4:  What is the probability we roll a number between 8 and 12 ?

Sol :                            P(8 < X <12 10="10" 11="11" 9="9" br="br" p="p">
                                     = 8/36 + 9/36 + 10/36

                                     = 27/36

         the probability we roll a number between 8 and 12 = 3/4