Respuesta :
Answer:
5.05% probability that no more than 34% had received such an email.
Step-by-step explanation:
We use the binomial approximation to the normal to solve this problem.
Binomial probability distribution
Probability of exactly x sucesses on n repeated trials, with p probability.
Can be approximated to a normal distribution, using the expected value and the standard deviation.
The expected value of the binomial distribution is:
[tex]E(X) = np[/tex]
The standard deviation of the binomial distribution is:
[tex]\sqrt{V(X)} = \sqrt{np(1-p)}[/tex]
Normal probability distribution
Problems of normally distributed samples can be solved using the z-score formula.
In a set with mean [tex]\mu[/tex] and standard deviation [tex]\sigma[/tex], the zscore of a measure X is given by:
[tex]Z = \frac{X - \mu}{\sigma}[/tex]
The Z-score measures how many standard deviations the measure is from the mean. After finding the Z-score, we look at the z-score table and find the p-value associated with this z-score. This p-value is the probability that the value of the measure is smaller than X, that is, the percentile of X. Subtracting 1 by the pvalue, we get the probability that the value of the measure is greater than X.
When we are approximating a binomial distribution to a normal one, we have that [tex]\mu = E(X)[/tex], [tex]\sigma = \sqrt{V(X)}[/tex].
In this problem, we have that:
[tex]n = 700, p = 0.37[/tex]
[tex]\mu = E(X) = np = 700*0.37 = 259[/tex]
[tex]\sigma = \sqrt{V(X)} = \sqrt{np(1-p)} = \sqrt{700*0.37*0.63} = 12.77[/tex]
In a random sample of 700 adults, what is the probability that no more than 34% had received such an email?
34% is 0.34*700 = 238
So this probability is the pvalue of Z when X = 238.
[tex]Z = \frac{X - \mu}{\sigma}[/tex]
[tex]Z = \frac{238 - 259}{12.77}[/tex]
[tex]Z = -1.64[/tex]
[tex]Z = -1.64[/tex] has a pvalue of 0.0505
5.05% probability that no more than 34% had received such an email.
