SOLUTION: Evaluate the expression a) 8C2 b) 8P2 Please help me on this. I need to understand , I have a final coming up.

Question 673581: Evaluate the expression
a) 8C2
b) 8P2
Please help me on this. I need to understand , I have a final coming up.

Answer by sachi(548) (Show Source): You can put this solution on YOUR website!
In general
nCr=n!/r!(n-r)!=n(n-1)(n-2)......3 2 1/r(r-1)!....2 1*(n-r)(n-r-1)...21
so 8C2=8!/2!6!=8*7*6*5*4*3*2*1/2*1*6*5*4*3*2*1=28
nPr=n!/(n-r)!=n(n-1)(n-2)......3 2 1/(n-r)(n-r-1)...21
so 8P2=8!/6!=8*7*6*5*4*3*2*1/6*5*4*3*2*1=56
ans
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