Question

Can someone break this down for me!! I'm stuck

it's an example the answer is 220

how do you get 220?!
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Answer 1

`_(12)C_9=220`

Explanation:

Recall the definition for the combination symbol with the use of factorial (symbol !):

`_nC_k=(n!)/(k!(n-k)!)`

Therefore, for the case where n = 12 and k = 9, we have:

`_(12)C_9=(12!)/(9!(3)!)\\_(12)C_9=(12*11*10*9*8*7*6*5*4*3*2)/(9*8*7*6*5*4*3*2(3*2))\\\\_(12)C_9=(12*11*10)/(3*2)\\\\_(12)C_9=(1320)/(6)\\\\_(12)C_9=220`