P(-2.14 < z < 0.95)
Notice that the shading below starts where z=-2.14 and goes to where z=0.95.
We want to know what decimal or percentage of the curve is shaded below
So by TI-83 or 84 calculator, we press " 2nd " then " vars " then " 2:normalcdf( "
[for newer calculators, lower:-2.14, upper:0.95, μ=0; σ=1; paste, enter]
For all calculators:
normalcdf(-2.14,0.95,0,1)
press ENTER
0.8127665627
With tables: [There are two kinds of tables in use today]
If your table has negative numbers in the z-column, then
find 0.9 in the z-column and go across to the 0.05 column and read 0.8289
find -2.1 in the z-column and go across to the 0.04 column and read 0.0162
Subtract and get 0.8289-0.0162 and get 0.8127
If your table has only positive numbers in the z-column, then
find 0.9 in the z-column and go across to the 0.05 column and read 0.3289
find 2.1 in the z-column and go across to the 0.04 column and read 0.4838
Add them and get 0.3289+0.4838 and get 0.8127
Notice that the calculator answers round to 0.8128, whereas with
tables you get 0.8127. That's because the calculator is more accurate
than tables.
Edwin
