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Earn 100

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)

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Important Questions on Permutations & Combinations

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If n distinct things are arranged in a circle, find the number of ways of selecting three of these things so that no two of them are next to each other.
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The number of different selections of 5 letters from 1A, 2B's, 3C's, 4D's and 5E's is :
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In the entrance test of Wharton Business School, the maximum marks for each of three papers is n and that for the fourth paper is 2n. Find the number of ways in which a candidate can get 3n marks.
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An examination consists of 4 papers. Each paper has a maximum of 'n' marks. Find the number of ways in which a students can get 2n marks in the examination.
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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 A and B if first A sends request to B then B will accept it or if first B sends request to A then A will accept it and thus both A and B 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?

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A king calls 11 masseurs for his queen, as she wants the body massage from Monday to Friday, while on weekends she wants to go on the long trips with the king. She wants everyday a new masseur, so basically 5 masseurs are required. But a confidant of the king tells him that out of 11 masseurs 5 are familiar with the queen before her marriage and she used to get very close to them. But the king has no idea of these 5 people who are familiar with the queen. In spite of knowing this very odd fact he takes the risk of telling the masseurs that they can start giving massage to his lovely queen, as he doesn't want to make any fuss over it. However, he wants to identify the 5 masseurs who are close to the queen. Based on the queen's personal behaviour with him the wise king gets an idea that if in any week out of the 5 familiar masseurs any 3 masseurs give the massage to the beautiful queen he will certainly identify who all these 5 people familiar with the queen are. Minimum how many weeks are required to identify these 5 masseurs familiar with the queen?
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There is a set of 10 integers {0,1,2,3,.,9}. In how many ways can you permute this set of integers such that either 3 and 6 or 5 and 4 or 6 and 5 appear consecutively?
(For example, we do not count (4,5,0,6,9,2,3,7,8,9), as we want 5 and 4 to appear consecutively in that order. But we count (7,2,0,1,4,3,6,5,8,9), both 3 and 6, and 6 and 5 appear consecutively in it.)
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How many integer solutions are there to the equation x1+x2+x3+x4=30, such that 3x1,x2,x3,x410.