Question 549761
how many possible ways to seat 15 kids in 15 seats?
Since ORDER matters, we have a permutation.  This means we want to get 15P15=15!/(15-15)!=15!


out of 15 students how many ways to choose 5 out of the 15 students for a project?
Since in this case order DOESN"T matter, we have a combination.  So we have 15C5 ways to do this.   (I will let you simplify using your combination formula).  

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Hopefully this helps! 
Romans 5:8