Mary S.

asked • 11/11/16

Math permutations & Combinations

Evaluate the expression.

C(10, 8) · C(9, 7)
C(11, 7)

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Inactive Tutor answered • 11/12/16

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It's time for you to do these calculations yourself, after having receiving copious help.
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Inactive Tutor

There are formulas for nPr and nCr; they rely on the definition of n! [pronounced n factorial]. These should be in your class notes or book.  Consult that material for examples. You can do it if you read carefully (repeat the reading as often as necessary).
 
There must be people who can help you in a one-on-one way, at whatever institution you are enrolled in.
 
C(n,r) is another format for nCr -- that is, two different notations for the same idea.
 
Do you have the manual for the graphing calculator?   
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11/13/16

Inactive Tutor answered • 11/11/16

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You submitted similar Permutation problems yesterday.

Today, just use the formula for Combinations.

nCr also known as C(n,r) = n! / [r!(n-r)!]

 
nCr work can be done on the calculator. 
 
By hand, 11C7 = 11(10)9(8) / 4! = 11(10)9(8)/ [4(3)2] = 11(80)(9) / [8(3)] =
11(10)3 =330
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