Answer to Question #223277 in Statistics and Probability for Lucky

Question #223277

For the production process of ballpoint pens of a certain type, it is known that 5% of the pens are

defective. The manager believes that this percentage is too high and hence changes the production

process. To test the merits of this new process, a random sample of 350 pens is taken; only 9 of

them are defective.

(a) (i) Determine a 90% confidence interval for p, the population proportion of defective pens

produced with the new process. (6)

(ii) Interpret the confidence interval. (2)

(iii) Do you think that the new process is better? (1)


1
Expert's answer
2021-08-12T18:22:20-0400

(a).

i. 90% confidence interval90\% \space confidence \space interval

CI=P^±z.(P^(1P^)n)CI=\hat P\pm z.(\sqrt{\frac{\hat P(1-\hat P)}{n}})

z=1.645z=1.645

P^=xn=9350=0.026\hat P=\frac{x}{n}=\frac{9}{350}=0.026\\

where x=9 (we use new value of defective , old value of defective is 5 % dont use in calculation of newprocess) n=350where \space x=9 \space (we \space use \space new \space value \space of \space defective \space , \space old \space value \space of \space defective \space is \space \\ 5 \space \% \space dont \space use \space in \space calculation \space of \space new-process)\\\space n=350

CI=0.026±1.645(9350(19350)350)CI=0.026\pm1.645(\sqrt{\frac{\frac{9}{350}(1-\frac{9}{350})}{350}})

=(0.012,0.04)=(0.012, 0.04)

0.012p0.04)0.012\le p\le0.04)


ii.

Therefore, based on the data provided , the  90% confidence interval for the population  proportion is Therefore, \space based \space on \space the \space data \space provided \space , \space the \space \space 90\% \\ \space confidence \space interval \space for \space the \space population \space \space proportion \space is \space \\

0.012P0.04)0.012\le P\le0.04)

which indicates that we are 90 %which \space indicates \space that \space we \space are \space 90 \space \%

confident that the true population proportion p is contained by the interval(0.012,0.04).confident \space that \space the \space true \space population \space proportion \\ \space p \space is \space contained \space by \space the \space interval (0.012,0.04).


iii.

The new  process is better since it lowers proportion  of defective pens significantly .The \space new \space \space process \space is \space better \space since \space it \space lowers \space proportion \space \space of \\ \space defective \space pens \space significantly \space .



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