Posted by Anonymous on Thursday, July 22, 2010 at 8:20pm.
The Academy of Orthopedic Surgeons states that 80% of women wear shoes that are too small for their feet. A researcher wants to be 98% confident that this proportion is within 3% of the true proportion. How large a sample is necessary?

Statistics  MathGuru, Friday, July 23, 2010 at 7:56pm
Try this formula:
n = [(zvalue)^2 * p * q]/E^2
...where n = sample size needed; use .8 for p and .2 for q (q = 1  p). E = maximum error, which is .03 (3%) in the problem. Zvalue is found using a ztable (for 98%, the value is 2.33). Also, ^2 means squared and * means to multiply.
I hope this will help get you started.
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