<PRE><B>Question 366920</B>
For their total production of light bulbs, the management of an electronics firm knows that the mean equals 150 hours. How large a sample is needed if they want to be 90% confident that the estimate of the average production time will be within 30 hours of the correct value? Does this have something to do with margin of error?
-------------
Yes.
Since ME = z*[s/sqrt(n)]
---
sqrt(n) = z*s/ME
----
n = [zs/ME]^2
----
Your Problem:

n = [1.645s/30]^2 where s is the standard deviation of the population.
===============
Cheers,
Stan H.
==========</PRE>