8.43 An advertising executive wants to estimate the mean amount of time that consumers spend with digital media daily. From past studies, the standard deviation is estimated as 45 minutes. a. What sample size is needed if the executive wants to be 90% confident of being correct to within {5 minutes

a

The sample size is  

b

The  sample size is  

Step-by-step explanation:

From the question we are told  that

    The standard deviation is  

    The  Margin of  Error is  

Generally the margin of  error is mathematically represented as

Where  n is the sample  size

    So

Now  at  90%  confidence level the z value for the z-table is  

        z =  1.645

So

The z-value at 99%  confidence level is  

This is obtained from the z-table  

   So the sample size is