# Stats Question

Six Sigma – iSixSigma Forums Old Forums General Stats Question

Viewing 7 posts - 1 through 7 (of 7 total)
• Author
Posts
• #47025

April
Participant

Can anyone help me understand how to get the answer for the following question?
Given the data below and the following requirements: Spec target 0.500. Any rivet must be within + .004. Assume normal distribution. What percentage of rivets is outside lower specification limit?
N       Mean         Median        TrMean      StDev         SE Mean
100    0.50011     0.50023      0.50013     0.00508      0.00051

0
#156186

veronabill
Member

If you use the raw data, the answer can be determined simply enough using minitab, stat/quality tools/capability analysis / normal nad input the appropriate data columns and sd estimate.

I created a random distribution of 100 numbers using the distribution parameters you supply, and the analysis indicates that about 20.6% of your parts are below the lower spec.

0
#156187

April
Participant

Would it be possible to determine without the raw data somehow?  This question was in some training material but the data is not there.
Thanks!

0
#156188

Craig
Participant

Calculate Z for the lower side (Mean – LSL / stdev)
Calculate tail area from Z table.

0
#156191

BritW
Participant

Z=.809
Prob=.3153 or 31.53%

0
#156192

walden
Participant

The calculated z-value is -0.809. There would be 18.67% below the LSL.
z-value = (.496-.50011)/.00508  or -0.809
Look up -0.809 in the standard normal curve table and you get .1867.

0
#156247

BritW
Participant

The formula for Z for a lower specification is:
(Mean-LSL)/SD = +.809
P(d) from the Z table is .8133

Z for the upper side is (USL-Mean)/SD

0
Viewing 7 posts - 1 through 7 (of 7 total)

The forum ‘General’ is closed to new topics and replies.