Question

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

	SCE	SCG
Sample Size	9	12
Sample Mean	3.2 minutes	2.8 minutes
Sample Standard Deviation	0.5 minutes	0.7 minutes

Test whether there is a significant difference in average time a customer is on hold between the two companies, at the level of significance 0.1.

Group of answer choices

A) Since 0.05 < p-value < 0.1, one cannot conclude that there is a significant difference in mean time a customer is on hold between the two companies.

B) Since 0.05 < p-value < 0.1, one can conclude that there is a significant difference in mean time a customer is on hold between the two companies.

C) Since 0.1 < p-value < 0.2, one can conclude that there is a significant difference in mean time a customer is on hold between the two companies.

D) Since 0.1 < p-value < 0.2, one cannot conclude that there is a significant difference in mean time a customer is on hold between the two companies.

Answer 1

	SCE	SCG
sample mean x =	3.200	2.800
standard deviation s=	0.500	0.700
sample size n=	9	12
Pooled Variance Sp2=((n1-1)s21+(n2-1)*s22)/(n1+n2-2)=			0.3889
Pooled Std dev Sp=√((n1-1)s21+(n2-1)*s22)/(n1+n2-2)=			0.6237
Point estimate : x1-x2=		0.4000
std. error se =Sp*√(1/n1+1/n2)=		0.2750
test stat t =(x1-x2-Δo)/Se=		1.455
p value : =		0.1620	from excel: tdist(1.455,19,2)

since p value >0.10 ; option D is correct

D) Since 0.1 < p-value < 0.2, one cannot conclude that there is a significant difference in mean time a customer is on hold between the two companies.