Computing areas under the Normal Curve with the TI-81
The program listed below will allow the user to find areas under the normal
curve for intervals ranging from -4.5 to 4.5. The results are reported
as percentages (0 to 100%) rounded to two places past the decimal (e.g.
The results are fairly accurate, with worst-case errors of 0.02%.
For the mathematically inclined, the algorithm simply evaluates
an eighth-degree polynomial approximation of the cumulative density function
at the two endpoints and subtracts. The polynomial approximation
is based on mutually orthogonal polynomials on [-4.5,4.5].
Just enter this program in your TI-81 and run. Please proofread
your typing carefully; being off by just one character will likely cause
Last Modified May 5, 1999.
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