P-chart with probability limits. Please help.

1. A process produces rubber belts in lots of size 2500. Inspection records on the last 20 lots reveal

the following data:

Lot number No. of nonconforming belts Lot number No. of nonconforming belts (The spacing is a bit messed up since I copied and pasted)

1 230 11 256

2 235 12 294

3 221 13 285

4 246 14 231

5 230 15 198

6 227 16 216

7 285 17 231

8 211 18 269

9 242 19 221

10 208 20 207

a. Set up a p- chart with 3 sigma limits to control the process. Estimate the process fraction

nonconforming. Is this an appropriate chart for this process? Explain.

b. Set up a p- chart with probability limits (α = 0.004 ) and estimate again the process fraction

nonconforming. Explain the difference between your answers in 1a) and 1b), if any.

OK. I understand part a. But have no clue about part b. Please help. If you can just tell me the methods or formulas that would be great.

Thank you.