nPr=\(\frac{n!}{(n-r)!}\)
9P3=\(\frac{9!}{(9-3)!}\)=
9!/6!=(987654321)/(654321) cancel=
(98*7)/(1)=504 ways
nCr=\(\frac{n!}{r!(n-r)!}\)
10C4=\(\frac{10!}{4!(10-4)!}\)=
\(\frac{10!}{4!(6)!}\)=
\(\frac{10*9*8*7*6*5*4*3*2*1}{4*3*2*1*6*5*4*3*2*1}\), cancel=
\(\frac{10*9*8*7}{4*3*2*1}\)=
\(\frac{2*5*3*3*2*4*7}{4*3*2*1}\)=
\(\frac{5*3*2*7}{1}\)=210
