Calculating a Standard Normal Probability or the Area Under the Standard Normal Curve
1. Finding :
The TI83/84 is equiped with a built in function called normcdf (,). It computes which is the area under the standard normal curve between and .
To calculate P(1 < z < 2), press 2nd VARS [DISTR], ARROW DOWN to select 2:normalcdf(, and then press ENTER.



After 2:normalcdf( type 1 2 ), and then press ENTER. See the results below.


To 4 decimal places, the P(1 < z < 2) = 0.8186.
2. Finding P(z < 2):
To calculate this probablity, P(z < 2), we can use the above normalcdf function since . Although we cannot enter as it is not a number, entering a very small number in its place, such as = E99, will do.
Press 2nd VARS [DISTR], ARROW DOWN to select 2:normalcdf(, and then press ENTER. Press then press 2nd [EE] and type 99. Press and type 2). Then press ENTER.



To 4 decimal places, the P (z < 2) = 0.9772.
To find P(z > 1) use the fact that P(z > 1) = P (1 < z < ). Using E99 for , we calculate normalcdf(1, E99). The result is shown below.
To 4 decimal places, the P (z > 1) = 0.1587.