NDA | Mathematics | P & C

There are 6 multiple choice questions in an examination. How many sequences of answer are possible if the first three questions have 4 choices each and next there have 5 each ?

In how many ways a 3-digit number can be formed from the digits 1, 4, 3, 6, 5 and 7, such that the number is divisible by 5 and none of the digits is being repeated?

If , find the value of n.

In how many ways seven different books be distributed to two persons if each person receives at least one book?

The number of ways in which a mixed double game can be arranged from amongst 9 married couples if no husband and wife play in the same game is