for calculating the value of choosing r items from n items where q are of same kind, and we should take %m , i used the following relation
(nPr/q!) %mwhere m is prime
For calculating this
i calculated
n!n!%mthen, i calculated
(n-r)!and multiplied it with q!, i.etemp = (n-r)!*q!;Then i mulitplied
modular mulitplicative inverseof temp with n! and took mod of resultbut am not getting the correct answer..E.g if n= 3 ; r = 2; q = 2 then the expected result is
(3P2/2!)%1000000007 = 3but am getting250000004..I can't understand my mistake here..Thanks.