I tried this Problem then i am able to get the dp relation dp[i][k]=(1/(i+1))*dp[i-1][k]+(i/(i+1))*dp[i-1][k-1] where dp[i][k] represent the probability of collection of k candies in first i bags . But here the value of N is very high so i am unable to solve it,that will be great help,Thanks in advance