EASY
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For any two events A, B if P(AB)=aP(AB)+bP(A)+cP(B), then 3a+2b+5c=?

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Important Questions on Permutation and Combination

EASY
There are m men and two women participating in a chess tournament. Each participant plays two games with every other participant. If the number of games played by the men between themselves exceeds the number of games played between the men and the women by 84, then the value of m is :
HARD
If i=120 20Ci-1 20Ci+20Ci-13=k21, then k equals
MEDIUM
The number of natural numbers less than 7000 which can be formed by using the digits 0, 1, 3, 7, 9 (repetition of digits allowed) is equal to:
HARD
Let A=x1,x2,,x7 and B=y1,y2,y3 be two sets containing seven and three distinct elements respectively. Then the total number of functions f:AB that are onto, if there exist exactly three elements x in A such that fx=y2, is equal to:
MEDIUM
There are 3 sections in a question paper and each section contains 5 questions. A candidate has to answer a total of 5 questions, choosing at least one question from each section. Then the number of ways, in which the candidate can choose the questions, is
EASY
The number of ways of selecting 15 teams from 15 men and 15 women, such that each team consists of a man and a woman is
EASY
Consider three boxes, each containing 10 balls labelled 1, 2, ., 10. Suppose one ball is randomly drawn from each of the boxes. Denote by ni, the label of the ball drawn from the ith box, i=1, 2, 3. Then, the number of ways in which the balls can be chosen such that n1<n2<n3 is :
EASY
Two women and some men participated in a chess tournament in which every participant played two games with each of the other participants. If the number of games that the men played between them-selves exceeds the number of games that the men played with the women by 66, then the number of men who participated in the tournament lies in the interval
MEDIUM
Suppose four balls labelled 1, 2, 3, 4 are randomly placed in boxes B1, B2, B3, B4. The probability that exactly one box is empty is
MEDIUM
The number of integers greater than 6000 that can be formed, using the digits 3, 5, 6, 7 and 8, without repetition is 
MEDIUM
The number of numbers between 2,000 and 5,000 that can be formed with the digits 0, 1, 2, 3, 4 (repetition of digits is not allowed) and are multiple of 3 is
HARD
Find the largest positive integer N such that the number of integers in the set {1,2,3,,N} which are divisible by 3 is equal to the number of integers which are divisible by 5 or 7 (or both).
MEDIUM
A man X has 7 friends, 4 of them are ladies and 3 are men. His wife Y also has 7 friends, 3 of them are ladies and 4 are men. Assume X and Y have no common friends. Then the total number of ways in which X and Y together can throw a party inviting 3 ladies and 3 men, so that 3 friends of each of X and Y are in this party is:
HARD
Let Tn be the number of all possible triangles formed by joining vertices of an n-sided regular polygon. If Tn+1-Tn=10, then the value of n is :
MEDIUM
From 6 different novels and 3 different dictionaries, 4 novels and 1 dictionary are to be selected and arranged in a row on the shelf so that the dictionary is always in the middle. Then the number of such arrangement is
HARD
The value of r=115r215Cr15Cr1 is equal to:
MEDIUM
If n+2C6n-2P2=11, then n satisfies the equation:
MEDIUM
A debate club consists of 6 girls and 4 boys. A team of 4 members is to be selected from this club including the selection of a captain (from among these 4 members) for the team. If the team has to include at most one boy, then the number of ways of selecting the team is
MEDIUM
If there are 5 letters written to 5 different people and 5 envelopes addressed to them, then the number of ways in which these letters can be arranged so that no letter goes into its corresponding envelope is
HARD
We will say that a rearrangement of the letters of a word has no fixed letters if, when the rearrangement is placed directly below the word, no column has the same letter repeated. For instance, HBRATA is a rearrangement with no fixed letters of BHARAT. How many distinguishable rearrangements with no fixed letters does BHARAT have? (The two A's are considered identical)