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Mathematics 13 Online
OpenStudy (anonymous):

medal! How many combinations of a president, vice-president, secretary, and treasurer can be chosen from a group of 12 students? 11,880 95,040 665,280 3,991,680

OpenStudy (luigi0210):

This is permutations correct?

OpenStudy (anonymous):

yesss

OpenStudy (anonymous):

@Luigi0210

OpenStudy (luigi0210):

Do you know the formula for permutations?

OpenStudy (anonymous):

yes nPr+ n!/ (n-2)

OpenStudy (luigi0210):

Just plug in values :)

OpenStudy (anonymous):

but the answer...we dont have this option

OpenStudy (anonymous):

!

OpenStudy (luigi0210):

Wait, nvm it's a combination!

OpenStudy (anonymous):

please just help me

OpenStudy (anonymous):

@Luigi0210

OpenStudy (dape):

Think of the different positions as 4 seats. For the first seat we can choose from 12 students, for the second we have 11 students left to choose from, continuing we get: \[ 12\times11\times10\times9=11880 \]

OpenStudy (dape):

This can also be written as \[ \frac{12!}{(12-4)!} \] Which hints at the general formula for permutations \[ \frac{n!}{(n-k)!} \] Where \(n\) is the number of choices have for each "seat" and \(k\) is the number of "seats".

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