How to calculate permutations on TI84 calculator?
Calculating permutations on a TI84 calculator can be done using the builtin nPr
(Permutation) function. Here's how you do it:

Access the Math Menu: Press the
MATH
button to access the Math menu. 
Select the Permutation Function: Use the arrow keys to navigate to the
PROB
column, and select2:nPr
and pressENTER
. This will open the permutation function.

Enter the Values:
 Enter the total number of items $n$.
 Enter the number of items to arrange $r$.

Perform the Calculation: After entering $n$ and $r$, press
ENTER
again to calculate the number of permutations.
The calculator will display the result, which is the number of ways to arrange $r$ items from a set of $n$ items where the order of selection matters.
Here's an example: If you want to calculate the number of permutations for arranging 3 items from a set of 5, you would:
 Press
MATH
to access the Math menu.  Choose
PROB
, select2:nPr
and pressENTER
.  Enter
5
for $n$ and3
for $r$.  Press
ENTER
to get the result.
The TI84 calculator will then display the number of permutations, which in this case is calculated using the formula $P(n, r) = \frac{n!}{(nr)!}$
, and for our example, it would be $\frac{5!}{(53)!} = 60$.
Remember that the permutation formula is $\frac{n!}{(nr)!}$, where $!$ denotes factorial, and $r$ is typically less than or equal to $n$. The calculator performs this calculation for you when you use the nPr
function.