Hi,

95% confident of estimating the population mean to within a sampling error of ± 2

ME = 1.96

2 = 1.96



     n = (1.96*13/2)^2

     n = 162.3076, 163 rounded up



	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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