P-Chart: Diff. btwn lot & sample size

[axnman]

Hi

need some clearance of idea:

A process produces rubber belts in lots of sizes 2,500. Inspection records on
the last 20 lots reveal the following data:

then u have data in the format:

Lot Number non-conforming belts
1 230
2 235
etc etc etc etc
20 207

need to calculate p-chart for it...so have p-bar = tot. defective/2500*20...right?

what would I use as "n" to calculate the control limits? n is sample size so should it be 2500(lot-size here?).

Would appreciate if anyone could clear it out for me

 

[HallsofIvy]

If all you have is what you have given here is all you have, you don't have enough information. In particular, knowing that there were 230 defectives in the sample tells you nothing if you don't know the size of the sample. 230 defectives out of a sample of 2500 might not be too bad but 230 defectives out of a sample of 230 surely is! Are you not told how large each sample is?