Answer :
[tex]\bf _{n}P_{r}=\cfrac{n!}{(n-r)!}\qquad \qquad _{11}P_4=\cfrac{11!}{(11-4)!}
\\\\\\
_nC_r=\cfrac{n!}{r!(n-r)!}\qquad \qquad _9C_5=\cfrac{9!}{5!(9-5)!}
[/tex]
check your calculator on the factorial(!) button.
check your calculator on the factorial(!) button.