A customer service representative was interested in comparing the average time (

Question

A customer service representative was interested in comparing the average time (in minutes) customers are placed on hold when calling Southern California Edison and Southern California Gas companies. The representative obtained two independent random samples and calculated the following summary information: So Cal Edison

Southern Cal Edison

Southern Cal Gas

Sample Size

9

12

Sample Mean

3.2 min

2.8 min

Sample Standard deviation

0.5 min

0.7 min

Assume the distributions of time a customer is on hold are approximately normal.

Using the null and alternate hypothesis:

H0:mu1-mu2=0 vs. Ha:mu1-mu2 not equal 0

The test statistic was computed to be -1.455

Assuming alpha = 0.10, set up the appropriate rejection region for the hypothesis test.

Reject H0 if |t| > t(alpha =0.1, df=20)

Reject H0 if |t| > t(alpha =0.05, df=19)

Reject H0 if |t| > t(alpha =0.05, df=20)

Reject H0 if |t| > t(alpha =0.1, df=19)

Southern Cal Edison

Southern Cal Gas

Sample Size

9

12

Sample Mean

3.2 min

2.8 min

Sample Standard deviation

0.5 min

0.7 min

Explanation / Answer

df = n1 + n2 -2 = 9 + 12 -2 = 19, also this is 2 tailed so we have to see t (0.05) instead of t(0.1)

Reject H0 if |t| > t(alpha =0.05, df=19)

Reject H0 if |t| > t(alpha =0.05, df=19)

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