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Confidence Intervals (easy question)

by Goalie_Ca
Tags: confidence, intervals
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Jul24-04, 08:48 PM
P: 105
Easy question but i'm being stupid somewhere. quite frustrating... enough to post it :surprise:

Basically the question is

Semiconductor wafer testing:
365 dies, 201 passed probing.
Assuming stable process calculate a 95% confidence interval for the proportion of all dies that pass the probe.

So x_bar = 201/365
std_dev = p*(1-p) = .228

the answer in the book is .513,.615 and i'm not getting that. same for the next question and the one after lol.

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Jul26-04, 07:47 AM
Sci Advisor
PF Gold
P: 39,327
The answer you say is in the book can't be right because it is not centered on the sample average: 201/365= 0.551 ((.513+ .615)/2= .564). Also your formula for standard deviation is wrong: you need a squareroot. Although I suspect it is a typo, is n 356 or 365?

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