SOLUTION: ncr=220 and npr=1320 find n and r

SOLUTION: ncr=220 and npr=1320 find n and r

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Question 479742: ncr=220 and npr=1320 find n and r
Answer by edjones(8007) (Show Source): You can put this solution on YOUR website!
nCr=n!/((n-r)!r!), nPr=n!/(n-r)!
nCr=nPr/r!
nCr*r!=nPr
220*r!=1320
r!=6
r=3
nP3=n!/(n-3)!=1320
n*(n-1)*(n-2)=1320
n^3-3n^2+2n=1320
n^3-3n^2+2n-1320=0
n=12
.
Ed
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