Question 670683
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Hi,
finding p-value after determining the correct z-value (or visa-versa)can be done:
I. using a chart
II. TI calculator
III.  Excel function 
a) z = 3  &#8658;  p = .999   Or  99.9% &#8804; 13.3oz 
What proportion of the packages will contain <u>more than 13.3 oz</u> of cereal?
 1- .999 = .001   Or 1%
Calculate the 85th percentile and interpret the result. 
IF  P = .85 &#8658; z = 1.04
 1.04 = (x - 13)/.1
  .104 + 13 = x
 13.104 = x, the 85th percentile

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 , 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))}}}