probability of 2 distributions

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probability of 2 distributions
Message posted by rob on June 23, 2000 at 12:00 AM (ET)

suppose i have a engine with bores w/ a mean of 25 & std of .002, and i have pistons with a mean of 24.5 & std of .002. what is the probability of finding 2 that will not work. .0001 or more is considered a interferance fit. NOTE both processes are feed to the assy station randomly & parts CAN NOT be pre measured or sorted.

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Re: probability of 2 distributions
Message posted by Phil on June 26, 2000 at 12:00 AM (ET)

With your numbers, the probability of an interference fit is practically zero without doing any calculations. However, statistically speaking, you need the distribution of Xbore-Xpiston. Which is Normal (mean=0.5, std.dev. = .0028). Use the normal table to find the probability that Xbore-Xpiston < 0.0001

(The variance of the difference assumes independence. The variance of the difference is the sum of the variances of the two variances.)

Another approach is to use simulation.

I would be interested to see if anyone has a different approach.

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