so if I want to find the 90% confidence interval..how do I do it?(adsbygoogle = window.adsbygoogle || []).push({});

all I know is that given 220 salads, 179 were contaminated.

i'm asked to find the 90% confidence interval, the true proportion of the contimatned salads.

so the formula is 100(1- a)% confidnece =[(y - z(a/2) * sigma/root(n)), ((y + z(a/2) * sigma/root(n)].

so my a is .9 right? since I am looking for 90%? so do I just do Z(.9/2) and look at the table?

what about n and sigma? n is 220, and what is sigma? what about the y's

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# Homework Help: Confidence intervals how to find?

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