How's the economy? A pollster wants to construct a confidence interval for the proportion of adults who believe that economic conditions are getting better. Part: 0 / 20 of 2 Parts Complete Part 1 of 2 (a) A poll taken in July estimates this proportion to be . Using this estimate, what sample size is needed so that the confidence interval will have a margin of error of ? A sample of adults is needed to obtain a confidence interval with a margin of error of .

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Complete Question

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Answer:

a

The sample size is [tex]n =944[/tex]

b

The sample size is [tex]n_b = 1068[/tex]

Step-by-step explanation:

From  the question we are told that

   The proportion is mathematically represented as  [tex]\r p = 0.33[/tex]

    The marginal error is  [tex]e = 0.03[/tex]

     The confidence level is  95 %  = 0.95

The z-value of the confidence level is

         [tex]z_c = 1.96[/tex]

This value is obtained from the z table

     The sample size is mathematically evaluated as

            [tex]n = [\frac{z_c}{e} ]^2 * \r p(1- \r p)[/tex]

substituting values

             [tex]n = [\frac{1.96}{0.03} ]^2 * 0.33 (1- 0.33)[/tex]

             [tex]n =944[/tex]

If no estimate is available the let assume  [tex]\r p = 0.50[/tex]

     So  

              [tex]n_b = [\frac{z_c}{e} ]^2 * \r p(1- \r p)[/tex]

substituting values

              [tex]n_b = [\frac{1.96}{0.03} ]^2 * 0.50 (1- 0.50)[/tex]    

               [tex]n_b = 1068[/tex]