Question

A Department of Transportation survey showed that 60% of U.S. residents over 65 years of age oppose use of cell phones in flight even if there were no issues with the phones interfering with aircraft communications systems. If this information is correct and if a researcher randomly selects 25 U.S. residents who are over 65 years of age?

a. What is the probability that exactly 12 oppose the use of cell phones in flight?
b. What is the probability that more than 17 oppose the use of cell phones in flight?
c. What is the probability that less than eight oppose the use of cell phones in flight? If the researcher actually got less than eight,what might she conclude about the Department of Transportation survey?

Answer 1

Answer:

a) $P(X=12)=(25C12)(0.6)^{12} (1-0.6)^{25-12}=0.0760$

b) $P(X>17) = P(X=18) +....+P(X=25)$

And we can use the following excel code: "=1-BINOM.DIST(17;25,0.6,TRUE)"

And we got:

$P(X>17) = P(X=18) +....+P(X=25)= 0.154$

c) $P(X<8) = P(X \leq 7)$

And using the following excel code we got: "=BINOM.DIST(7,25,0.6,TRUE)"

And we got:

$P(X<8) = P(X \leq 7) =0.0012$

Step-by-step explanation:

Previous concepts

A Bernoulli trial is "a random experiment with exactly two possible outcomes, "success" and "failure", in which the probability of success is the same every time the experiment is conducted". And this experiment is a particular case of the binomial experiment.

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".

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:  

$nCx=\frac{n!}{(n-x)! x!}$  

The complement rule is a theorem that provides a connection between the probability of an event and the probability of the complement of the event. Lat A the event of interest and A' the complement. The rule is defined by: $P(A)+P(A') =1$

Solution to the problem

Part a

$P(X=12)=(25C12)(0.6)^{12} (1-0.6)^{25-12}=0.0760$

Part b

For this case we want this probability:

$P(X>17) = P(X=18) +....+P(X=25)$

And we can use the following excel code: "=1-BINOM.DIST(17,25,0.6,TRUE)"

And we got:

$P(X>17) = P(X=18) +....+P(X=25)= 0.154$

Part c

For this case we want this probability:

$P(X<8) = P(X \leq 7)$

And using the following excel code we got: "=BINOM.DIST(7,25,0.6,TRUE)"

And we got:

$P(X<8) = P(X \leq 7) =0.0012$