Example (TI83): Find the probability that 3 successes will occur if
the average number of successes is 3/4. That is, find P(x = 3). 

Press 2^{nd} VARS [DISTR]. Scroll down to C:poissonpdf( Press ENTER. 

Enter 3/4,3) and press ENTER to get the answer .03321. The syntax is poissonpdf(mean, xvalue). 

Example (TI83): Find the probability that 3 or less successes will
occur if the average number of successes is 3/4. That is, find P(x ≤ 3). 

Press 2^{nd} VARS [DISTR]. Scroll down to D:poissoncdf( Press ENTER. 

Enter 3/4,3) and press ENTER to get the answer .9927. The syntax is poissioncdf(mean, largest xvalue). 

Example (TI83): Find the probability that at least 3 successes
will occur if the average number of successes is 3/4. That is, find P(x ≥
3). Use the complement rule to find
P(x ≥ 3) = 1 – P(x ≤ 2). 

Press 1 – and 2^{nd} VARS [DISTR]. Scroll down to D:poissoncdf( Press ENTER. 

Enter 3/4,2) and press ENTER to get the answer .0405. The syntax is 1 – poissoncdf(mean, largest xvalue). 