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 $171 per month. A random sample of 60 customers was selected during the winter of 2009-2010, and the average bill was found to be $162.99 with a sample standard deviation of $22.48. Complete parts a and b below. Click here to view page 1 of the Student's t-distribution table. Click here to view page 2 of the Student's a) Using a0.05, 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. O A. Hows 171 and H1 : > 171 O B. Ho: 2 171 and H1 :

Explanation / Answer

The statistical software output for this problem is:

One sample T summary hypothesis test:
: Mean of population
H0 : = 171
HA : < 171

Hypothesis test results:

Hence,

a) Hypotheses: Option B is correct.

Critical value = -1.671

Test statistic = -2.76

Conclusion: Option C is correct.

b) Option D is correct.

Mean Sample Mean Std. Err. DF T-Stat P-value 162.99 2.9021555 59 -2.7600175 0.0038

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