A large bank believes that one-third of its checking customers have used at least one of the bank's other services during the past year. How large a sample is required to estimate the actual proportion within a range of plus and minus 0.04? Use the 98 percent level of confidence.

Answer 1

Try this formula:
n = [(z-value)^2 * p * q]/E^2
...where n = sample size needed; z-value is found using a z-table; p = 1/3; q = 2/3; E = .04

Determine the z used for 98% confidence by checking a z-table. Convert all fractions to decimals. Plug values into the formula to determine n. Round answer to the next highest whole number.

I hope this will help get you started.