Hi, 

50 calls initiated on cellular car phones with mean duration of 3.5 minutes & SD = 1.2 minutes

Find 99% confidence interval for the mean duration of telephone calls initiated on a cellular car phone.

  ME =  = .437

 CI: 3.5-.437> u < 3.5+.437

 CI: 3.063 > u < 3.947

Note: -------------------------------------------------------------

	a	a/2	crtical regions	

80%	0.2	10%	z <-1.28155	z >+1.28155

90%	0.1	5%	z <-1.645	          z >+1.645

92%	0.8	4%	z <-1.751	          z >+1.751

95%	0.05	2.50%	z <-1.96	          z >+1.96

98%	0.02	1%	z <-2.33	          z >+2.33

99%	0.01	0.50%	z<-2.576	          z >+2.576

 

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