During the winter of 2008-2009, the average utility bill for residents of a cert

Question

During the winter of 2008-2009, the average utility bill for residents of a certain state was $180 per month. A random sample of 30 customers was selected during the winter of 2009-2010, and the average bill was found to be $171.85 with a sample standard deviation of $22.12. Complete parts a and b below Click her Click her f the Student's t-distribution table a) Using = 0.05, does this sample provide enough evidence to conclude that the average utility bill in this state was lower in the winter of 2009-2010 than it was in the winder of 2008-2009? Determine the hypotheses 0 A. H04 180 and H1 : > 180 O B. Ho : #180 and H1:=180 C. Ho: = 180 and H1-180 OD. H042180 and H1:

Explanation / Answer

a) option d is correct

for (n-1=29) degree of freedom and 0.05 level critical value t =-1.699

std error of mean =std deviaiton/(n)1/2 =22.12/(30)1/2 =4.0385

tehreore test stat tx =(X-mean)/std error=(171.85-180)/4.0385=-2.018

conclusion:

option D

b)

option B

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