A manufacturing process produces steel rods in batches of 1,000. The firm believ
ID: 3439820 • Letter: A
Question
A manufacturing process produces steel rods in batches of 1,000. The firm believes that the percent of defective items generated by this process is 5%.
a.
Construct the centerline and the upper and lower control limits for the chart.
b.
An engineer inspects the next batch of 1,000 steel rods and finds that 6.2% are defective. Is the manufacturing process under control? Explain.
a.
Construct the centerline and the upper and lower control limits for the chart.
b.
An engineer inspects the next batch of 1,000 steel rods and finds that 6.2% are defective. Is the manufacturing process under control? Explain.
Explanation / Answer
Prob for defective in a batch = 5%
I.e. average defectives in a batch = 50
mu = 50
Variance = npq = 50(0.95)
=47.5
sigma =6.892
a) Centre line is the horizontal line mu =50
Upper control line =50+3(6.892)=70.676
Lower control line = 50-3(6.892)=29.324
-----------------------------------
6.2% defective means
no of defectives = 62
Obviously 62 lies between the upper and lower bounds.
Hence the manufacturing process is under control
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