nP5nC5=n!(n−5)!÷n!(n−5)!5!\frac{{}^{n}P_{5}}{{}^{n}C_{5}} = \frac{n!}{(n-5)!} \div \frac{n!}{(n-5)!5!}nC5nP5=(n−5)!n!÷(n−5)!5!n!
= racn!(n−5)!×(n−5)!5!n!=5!=120rac{n!}{(n-5)!} \times \frac{(n-5)!5!}{n!} = 5! = 120racn!(n−5)!×n!(n−5)!5!=5!=120
