Question 1159165: A shipping firm suspects that the mean life of a certain brand of tire used by its trucks is more than 40,000 miles. To check the claim, the firm randomly selects and tests 18 of these tires and gets a mean lifetime of 40503 miles with a standard deviation of 1200 miles. At α = 0.05, test the shipping firm's claim. Assume the distribution is normal. Use the P-value method. Exact value of the standard deviation is not known.
Answer by Boreal(15235)   (Show Source):
You can put this solution on YOUR website! this is a t-test (last statement)
Ho: brand lasts < 40000 miles
Ha: it lasts more
alpha=0.05 P{reject Ho|Ho true|
test statistic is a t 0.95, df=17
critical value is t> 1.74 for a one way test
calculation t=(x bar- mean)/s/sqrt(n)
=503*sqrt(18)/1200
=1.78
because t >1.74, can conclude the tires do last for more than 40,000 miles
p=0.0466
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