Hi, Re TY, Yes!  Good work! Two-tailed. 

How many people would need to be surveyed on health care to estimate the mean of an entire population to within 2 units 

if the standard deviation was 12 and we wanted a 92% confidence level?

92% confidence level ⇒ z = 

ME =  

    

        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 <-2.326	          z >+2.326

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

 

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