Question

In a recent survey of 25 voters, 17 favor a new city regulation and 8 oppose it. What is the probability that in a random sample of 6 respondents from this survey, exactly 2 favor the proposed regulation and 4 oppose it?

Answer 1

Answer:

$P(X=2)=(6C2)(0.68)^2 (1-0.68)^{6-2}=0.0727$

Step-by-step explanation:

1) Previous concepts

The binomial distribution is a "DISCRETE probability distribution that summarizes the probability that a value will take one of two independent values under a given set of parameters. The assumptions for the binomial distribution are that there is only one outcome for each trial, each trial has the same probability of success, and each trial is mutually exclusive, or independent of each other".

2) Solution to the problem

The probability in favor of the regulation based on the recent survey is:

$p = \frac{17}{25}=0.68$

Let X the random variable of interest "Number of favor respondents about the regulation", on this case we now that:

$X \sim Binom(n=6, p=0.68)$

The probability mass function for the Binomial distribution is given as:

$P(X)=(nCx)(p)^x (1-p)^{n-x}$

Where (nCx) means combinatory and it's given by this formula:

$nCx=\frac{n!}{(n-x)! x!}$

And we want to find this probability:

$P(X=2)=(6C2)(0.68)^2 (1-0.68)^{6-2}=0.0727$

If we use X= "Number of respondednts opposed to the regulation we got the same answer", but on this case p = 1-0.68=0.32, and we want this probability:

$P(X=4)=(6C4)(0.32)^4 (1-0.32)^{6-4}=0.0727$