(a).
i. 90% confidence interval
CI=P^±z.(nP^(1−P^))
z=1.645
P^=nx=3509=0.026
where x=9 (we use new value of defective , old value of defective is 5 % dont use in calculation of new−process) n=350
CI=0.026±1.645(3503509(1−3509))
=(0.012,0.04)
0.012≤p≤0.04)
ii.
Therefore, based on the data provided , the 90% confidence interval for the population proportion is
0.012≤P≤0.04)
which indicates that we are 90 %
confident that the true population proportion p is contained by the interval(0.012,0.04).
iii.
The new process is better since it lowers proportion of defective pens significantly .
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