The First National Bank of Wilson has 600 checking account c

The First National Bank of Wilson has 600 checking account customers. A recent sample of 70 of these customers showed 26 to have a Visa card with the bank.

Construct the 98 percent confidence interval for the proportion of checking account customers who have a Visa card with the bank. (Round your answers to 3 decimal places.)

Solution

Given a=1-0.98=0.02, Z(0.01)=2.33 (from standard normal table)

p=26/70 =0.3714286

So the lower bound is

p-Z*sqrt(p*(1-p)/n) =0.3714286-2.33*sqrt(0.3714286*(1-0.3714286)/70) =0.237

So the upper bound is

p+Z*sqrt(p*(1-p)/n) =0.3714286+2.33*sqrt(0.3714286*(1-0.3714286)/70) =0.506