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Permutations
Another common function needed to compute dependent probabilities that uses factorial is the
permutation formula. The number of permutations is normally written as nPr; on the calculator
with the symbol P written between n and r, where n is the total number of elements, and r is the
number being selected. Permutations are used when trying to find all possible arrangements of
elements taken from a larger selection.
Let’s say that you wanted to find the number of ways six people could be arranged in ten
different chairs. You could solve this by 10 nPr 6 .
Type in the number 10.
Press the MATH key.
Press the ► to highlight PRB.
Press the number 2 key.
Press the number 6 key.
Press the ENTER key to get the value 151200.
Combinations
Another similar function needed to compute dependent probabilities that uses factorial is the
combination formula. The number of combinations is normally written as nCr; on the calculator
with the symbol C written between n and r, where n is the total number of elements, and r is the
number being selected. Permutations are use when trying to find all possible groupings of
elements taken from a larger selection.
Example: Ice Cream
An ice cream parlor has six flavors of ice cream. Kristen wants to buy two flavors of ice cream.
If she randomly selects two flavors out of six, how many possible combinations are there?
In order to find the number of ways of choosing two flavors out of six, we would need to type
6 nCr 2. The symbol nCr is also found under MATH page under PRB.
Type in the number 6.
Press the MATH key.
Press the ► to highlight PRB.
Press the number 3 key.
Press the number 2 key.
Press the ENTER key to get the value 15.
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