How do you calculate combinations on the TI-84?

1 Answer
MeneerNask
Feb 9, 2015

I use a #TI-83+# but the procedure will be the same.

The procedure is called #nCr# and it means:
From a group of #n# you select #r# while the order is not important.

Say you want to choose 3 students as class-representatives from a class of 25:

Recipe
Type in #25#
Use the #MATH#-button and move to the #PRB#-menu (far right)
Choose #nCr# and #enter#
Type in #3# and #enter#
The answer (#2300#) will be the number of combinations.

BTW:
If the order is important (1st=president, 2nd=secretary, 3d=member), then you use #nPr# (=number of permutations) from the same menu (answer should be #13800#)

The ratio between the two is the number of different orders that this selection can be in. (in this case #3! =6#).
In other words: #nPr= nCr *r!#
Where #n# number to choose from, and #r# number to be chosen.

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