16.If the permutations of A,B,C,D,E taken all together be written down in alphabetical order as in dictionary and numbered, then the rank of the permutation DEBAC is

17.Six points in a plane be joined in all possible ways by indefinite straight lines and if no two of them be coincident or parallel and no three pass through the same point(with the exceptions of the original 6).The number of distinct points of intersection is equal to

18.Out of 8 sailors on a boat, 3 can work only on one side and 2 only on the other side. The number of ways the sailors can be arranged on the boat is

19.An n-digit number is a positive number with exactly n digits. Nine hundred distinct n-digit numbers are to be formed using only the three digits 2,5 and 7.The smallest value of N for which this is possible is

20.In an examination, there are three multiple choice questions and each question has 4 choices. Number of sequences in which student can fail to get all answers correct is