
Find the number of ways of putting five distinct rings on four fingers of the left hand. (Ignore the difference of size of rings and the fingers)


Important Questions on Permutations & Combinations




Mark Shekhar Garg goes to a school to demonstrate how the kids can use the Facebook harmlessly and take the optimum advantage of socialization with fellow kids online at the early age of their social being. He tells the kids, after demonstrating the usage and safety features, that to make someone your facebook friend you have to send her/him a request and the other person has to accept it; as in out of two classmates and if first sends request to then will accept it or if first sends request to then will accept it and thus both and will become facebook friends.
As every kid responds to his instructions, within a minute Mark finds that every student in the class is now facebook friend of the other. In that class the number of female students is twice that of male students. He also notices that the number of friend-requests sent by the female kids is equal to the number of friend-requests sent by the male kids. Which of the following can be the number of friend-requests sent by female students to male students of that class?


(For example, we do not count , as we want and to appear consecutively in that order. But we count , both and and and appear consecutively in it.)

