SOLUTION: 1. Yolanda has seven CDs that she is going to give away. She lets her best friend choose two of the seven CDs. How many different groups of two CDs are possible?

Question 1168477: 1. Yolanda has seven CDs that she is going to give away. She lets her best friend choose two of the seven CDs. How many different groups of two CDs are possible?
Answer by ikleyn(52781) (Show Source): You can put this solution on YOUR website!
.


In this problem, by DEFAULT, the order of the CDs in groups does not matter: 

    the group of two CDs (A,B) is the same as the group (B,A).



There are   = 7*3 = 21  such groups.

Such objects are called COMBINATIONS in Mathematics.

On Combinations, see introductory lessons
    - Introduction to Combinations
    - PROOF of the formula on the number of Combinations
    - Problems on Combinations
    - OVERVIEW of lessons on Permutations and Combinations
in this site.

Also, you have this free of charge online textbook in ALGEBRA-II in this site
    - ALGEBRA-II - YOUR ONLINE TEXTBOOK.

The referred lessons are the part of this online textbook under the topic "Combinatorics: Combinations and permutations".

Save the link to this textbook together with its description

Free of charge online textbook in ALGEBRA-II
https://www.algebra.com/algebra/homework/complex/ALGEBRA-II-YOUR-ONLINE-TEXTBOOK.lesson

into your archive and use when it is needed.

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