Question

For this problem, carry at least four digits after the decimal in your calculations. Answers may vary slightly due to rounding.

In a random sample of 60 professional actors, it was found that 42 were extroverts.

(a) Let p represent the proportion of all actors who are extroverts. Find a point estimate for p. (Round your answer to four decimal places.)

_____________
(b) Find a 95% confidence interval for p. (Round your answers to two decimal places.)

lower limit
upper limit

Give a brief interpretation of the meaning of the confidence interval you have found.

We are 5% confident that the true proportion of actors who are extroverts falls within this interval.

We are 95% confident that the true proportion of actors who are extroverts falls outside this interval.    

We are 5% confident that the true proportion of actors who are extroverts falls above this interval.

We are 95% confident that the true proportion of actors who are extroverts falls within this interval.

(c) Do you think the conditions np > 5 and nq > 5 are satisfied in this problem? Explain why this would be an important consideration.

No, the conditions are not satisfied. This is important because it allows us to say that p̂ is approximately binomial.

Yes, the conditions are satisfied. This is important because it allows us to say that p̂ is approximately normal.    

Yes, the conditions are satisfied. This is important because it allows us to say that p̂ is approximately binomial.

No, the conditions are not satisfied. This is important because it allows us to say that p̂ is approximately normal.

Answer 1

a)

Number of Items of Interest,   x =   42
Sample Size,   n =    60
      
point estimate of p = Sample Proportion ,    p̂ = x/n = 42/60 = 0.7000

b)

Level of Significance,   α =    0.05          

z -value =   Zα/2 =    1.960   [excel formula =NORMSINV(α/2)]      
                  
Standard Error ,    SE = √[p̂(1-p̂)/n] =    0.0592          
margin of error , E = Z*SE =    1.960   *   0.0592   =   0.1160
                  
95%   Confidence Interval is              
Interval Lower Limit = p̂ - E =    0.700   -   0.1160   =   0.5840
Interval Upper Limit = p̂ + E =   0.700   +   0.1160   =   0.8160
                  
95%   confidence interval is (   0.58 < p <    0.82 )
We are 95% confident that the true proportion of actors who are extroverts falls within this interval.

c)

Yes, the conditions are satisfied. This is important because it allows us to say that p̂ is approximately normal.