The TI-83 and higher calculators are equipped with two functions: BinomPDF and BinomCDF to help you make light work of figuring our binomial probabilities. While figuring out binomial distributions by hand can involve multiple equations and lots of time (especially if you are working with cumulative probabilities), entering a binomial probability into the TI 83 is no harder and entering an addition problem into the home screen. This article tells you how to use the BinomPDF function to figure out an exact quantity (like three times, or twice, or a dozen occurrences). For cumulative probabilities (like “up to a certain number” or “between 5 and 10″ or “under 6″ or something similar, you’ll want to check out this other article on TI 83 BinomCDF.
Sample problem: Sue has a batting average of .270. If she is at bat three times, what is the probability that she gets exactly two hits?
Step 1: Press 2nd VARS to get the “DISTR” option. Press 0 for “binomPDF.”
Step 2: Enter the number of trials from the question. Sue bats three times, so the number of trials is 3. Press 3 and hit the , key.
Step 3: Enter the Probability of Success, P. Sue’s batting average is .240, so enter .270, then hit the , key.
Step 4: Enter the X value. We want to know Sue’s chances of getting exactly two hits, so enter 2 and then press ).
Step 5: Press Enter for the result. Sue’s chances of getting exactly two hits is .159651.
Warning: BinomialPdf is an exact probability for one value of x. If you want to find a cumulative probability (for example, what are John’s chances of getting 0 or 1 hits?) you will need the use the BinomialCdf function.