Question 634832
  <pre><font face = "Tohoma" size = 3 color = "indigo"><b> 
Hi,
Find the z-scores for which 90% of the distribution's area lies between -z and z.
z = ± 1.751
 	a	a/2	2-tailed crtical regions	
80%	0.2	10%	z <-1.28155	z >+1.28155
90%	0.1	5%	z <-1.645	           z >+1.645
92%	0.08	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


Important to Understand z -values as they relate to the Standard Normal curve:
Below:  z = 0, z = ± 1, z= ±2 , z= ±3 are plotted.  
Note: z = 0 (x value the mean) 50% of the area under the curve is to the left and 50%  to the right
{{{drawing(400,200,-5,5,-.5,1.5, graph(400,200,-5,5,-.5,1.5, exp(-x^2/2)), green(line(1,0,1,exp(-1^2/2)),line(-1,0,-1,exp(-1^2/2))),green(line(2,0,2,exp(-2^2/2)),line(-2,0,-2,exp(-2^2/2))),green(line(3,0,3,exp(-3^2/2)),line(-3,0,-3,exp(-3^2/2))),green(line( 0,0, 0,exp(0^2/2))),locate(4.8,-.01,z),locate(4.8,.2,z))}}}