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Combinatorics formulas Practice
Combination, permutation, and two-stage counting relationships.
Start practicingCombinatorics formulas
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What you’ll practice
Decide whether order matters and whether repetition is allowed before choosing a counting formula. The same objects can give different counts under different rules.
Where this helps
Distinguishing selections where order matters from those where it does not.
Before you start
Use this topic to practice math you have already learned. The examples show the available kinds of recall tasks; this is not a complete textbook chapter. Check the answer form and any stated conditions.
Try a few examples
Real practice. Real progress.
Example 1 of 3
n and r are integers with 0 <= r <= n and factorial uses nonnegative-integer arguments.
Choose the exact expression.
Grades and courses that include this topic
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Start practicingCombinatorics formulas
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