# 22: Combinations

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• 22.1: Motivation
How many different four-member study groups could be formed from a class of twenty students?
• 22.2: Basics
Combination: a finite subset of a given set
• 22.3: Applications
How many ways are there to distribute seven coins amongst three children? (Assume the coins are indistinguishable. But children are obviously distinguishable.)
• 22.4: Properties
Note: In this section we will use the alternative notation Cnk in place of C(n,k).
• 22.5: Activities
• 22.6: Exercises

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