Question 621444
  <pre><font face = "Tohoma" size = 3 color = "indigo"><b> 
Hi,
Note:  Bell shaped Curve showing placement of z = 0, z = ±1, 2, 3 
Left or Right of z = 0 being 50% of the area under the standard normal curve...
{{{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))}}}
As to A set of data is normally distributed with a mean of 100 and SD of 15. <span style="text-decoration: overline">X</span> = 90 
 z = (90-100)/15 ={{{ -.6667}}}
Exel function NORMSDIST(-.6667) = .25 , 25% to the left and 75% to the right
What percentage of scores is between 100 and 90? 25%
· What would be the percentile rank for a score of 90? 25%
{{{drawing(400,200,-5,5,-.5,1.5, graph(400,200,-5,5,-.5,1.5, 0,exp(-x^2/2)), blue(line( -.6667,0, -.6667,exp(-.6667^2/2))),locate(4.8,-.01,z),locate(4.8,.2,z))}}}