Question

How to solve for n using my knowledge of permutations

Answer 1

NP5=18*N-2P4
N!/(N-5)!=18*(N-2)!/(N-6)!

(N(N-1)(N-2)!)/(N-5)*(N-6)!=18*(N-2)!/(N-6)!
N(N-1)/N-5=18
N^2-N=18N-90
N^2-19N-90=0
N=9,N=-10
-10 is not possible so N=9