# constructing a confidence interval

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• April 10th 2010, 06:59 AM
kesk717
constructing a confidence interval
among 500 marriage license applications chosen at random, there were 48 in which the woman was at least 1 year older than the man, and among 400 marriage license applications chosen at random 6 years later, there were 68 in which the woman was at least 1 year older than the man. Construct a 99% confidence interval for the difference between the corresponding true proportions of marriage license applications in which the woman was at least 1 year older than the man.

Could use some assistance on this. Thank you for anyone who can help me.
• April 10th 2010, 08:22 PM
matheagle
$(.096 -.17)\pm z_{.005}\sqrt{ {(.096)(1-.096)\over 500}+ {(.17)(1-.17)\over 400}}$

where $z_{.005}=2.5776$ from http://bayes.bgsu.edu/nsf_web/jscrip...ormal_icdf.htm