Calculating a value for the value of P( z < )

1. Finding z:

The TI-83/84 is equiped with a built in function called invNorm (p). It computes where p = P(z < ) which is the area under the standard normal curve between to the left of .

To calculate z for a p = 0.9, that is the area under the standard normal curve is 0.9 and this area is to the left of some z value, press 2nd VARS [DISTR], ARROW DOWN to select 3:invNormal(, and then press ENTER.

After 3:invNormal( type .9), and then press ENTER. See the results below.

To 4 decimal places, z = 1.2816, and 90% of the z values lie below this amount.