A manufacturer of coil spring is interested in implementing a quality control system to monitor his production process. As part of this quality system, it is decided to record the number of nonconforming springs in each production batch of size 50. During 40 days of production, 40 batches of data were collected and follow: Batch No. No. of Nonconforming Springs 19 212 36 49 57 614 712 84 96 107 118 125 139 147 158 1611 173 186 197 207 2111 224 234 248 257 265 276 284 295 308 3119 3219 3318 3412 3511 3617 3715 3817 3913 4013
Let X be a random variable representing the number of nonconforming coil springs in a production batch of size 50. Its mean is denoted µ and its standard deviation is ?.
a. Give a point estimate for µ and ?.
b. Compute the (estimated) standard error for the estimate of the mean.
c. Construct a 95% confidence interval for µ.
d. Without computing the 90% confidence interval for µ, would you expect the length of the interval to be smaller or larger than the 95% confidence interval? Explain your answer in a few sentences.