Question: how to calculate permutations and combinations on calculator?
Answer: Step 1: Type in the first number. In this case, the first number is 25.
Step 2: Press [MATH] and go to the PRB menu. You can use the right arrow to select the menu at the top.
Step 3: Select 3 nCr and press [ENTER] ... 
Step 4: Type the second number and press [ENTER]