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posted by johnny on .
The Ledd Pipe Company has received a large shipment of pipes, and a quality control inspector wishes to
estimate the average diameter of these pipes. A random sample of 18 pipes produces an average diameter of
2.56 mm with a standard deviation of 0.05 mm.
The average diameter of the pipes must not differ significantly from 2.52 mm. Is there enough evidence at
the 5% level of significance to conclude that the true average diameter differs from this amount? Conduct an
appropriate hypothesis test using (i) the pvalue method, (ii) the rejection point method, and (iii) the confidence
interval method.

n = 18
xbar = 2.56 s = 0.05
H0 : mu = 2.52 H1: mu not equal 2.52
test stat = t = (xbarmu)/(s/sqrt(n)) = 3.39
pvalue = 0.003 < 0.05 Reject H0
tcritical = 2.11 < 3.39 Reject H0
CI =(xbartcritical*s/sqrt(n), xbar+tcritical*s/sqrt(n))
(2.54, 2.58)