If n-1P3 : n+1P3= 5:12 , find n. Share with your friends Share 10 Neha Sethi answered this Dear student Given , Pn-1,3:P(n+1,3)=5:12,⇒ Pn-1,3P(n+1,3)=512⇒(n-1)!(n-1-3)!(n+1)!(n+1-3)!=512⇒(n-1)!(n-4)!(n+1)!(n-2)!=512⇒(n-1)!(n-4)!×(n-2)!(n+1)!=512⇒(n-1)!(n-4)!×(n-2)(n-3)(n-4)!n(n+1)(n-1)!=512⇒(n-2)(n-3)n(n+1)=512⇒n2-3n-2n+6n2+n=512⇒n2-5n+6n2+n=512⇒12n2-60n+72=5n2+5n⇒7n2-65n+72=0⇒n=65±652-477227n=65±4225-201614n=65±4714n=8 or n=97 which is not possible.So, n=8 Regards 23 View Full Answer
