Question 324239
A recent survey of gasoline prices indicated that the national average was $4.098 per gallon. The Dallas Automobile Club claimed that gasoline in Texas was significantly lower than the national average. 
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Note: "lower than" implies a left tail test
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A survey covering 10 different suburbs in Dallas found the average price of gasoline to be $3.924 per gallon with a population standard deviation of $0.053. 
Note: n = 10, so df = 9
What critical value should be used to test the claim using α = 0.01?
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Note: Critical value is a 1% right tail of the t-distribution when df=9. 
Using a TI-84 I get invT(0.99 with df=9) = 2.8214
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Cheers,
Stan H.