Confidence Intervals (easy question)

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SUMMARY

The forum discussion revolves around calculating a 95% confidence interval for the proportion of semiconductor dies that pass probing, based on a sample of 365 dies with 201 passing. The user calculates the sample proportion as x_bar = 201/365 = 0.551 and identifies a discrepancy with the book's answer of 0.513 to 0.615. The user also points out an error in the standard deviation formula, emphasizing the need for a square root in the calculation. The confusion regarding the sample size, questioning whether it is 356 or 365, further complicates the issue.

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Goalie_Ca
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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
n=356.

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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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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