SOLUTION: Some manufacturers claim that non-hybrid sedan cars have a lower mean miles-per-gallon (mpg) than hybrid ones. Suppose that consumers test 21 hybrid sedans and get a mean of 31 mpg

Question 1194813: Some manufacturers claim that non-hybrid sedan cars have a lower mean miles-per-gallon (mpg) than hybrid ones. Suppose that consumers test 21 hybrid sedans and get a mean of 31 mpg with a standard deviation of seven mpg. 18non-hybrid sedans get a mean of 22 mpg with a standard deviation of four mpg. At 0.05 level of significance, conduct a hypothesis test to evaluate the manufacturers claim.
Answer by Boreal(15235) (Show Source): You can put this solution on YOUR website!
Ho: NH>= H
Ha: NH< H
alpha=0.05 p{reject Ho|Ho true}
test statistic is a t (0.95, df=37)
critical value is t < -1.687
t=(NH-H)/sqrt (sH^2/n1)+(sNH^2/n2)
=-9/sqrt((49/21)+(16/18))
=-9/1.80
=-5
strongly reject Ho and conclude that the manufacturer's claim is correct.
p <0.0001

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