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In order to get through in an examination of nine papers, a candidate has to pass in more papers than the number of papers in which he fails. The number of ways in which he can fail in this examination is:

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Important Questions on Permutation and Combination

MEDIUM
In a group of 8 girls, two girls are sisters. The number of ways in which the girls can sit so that the two sisters are not sitting together is
HARD
Six persons A, B, C, D, E and F are to be seated at a circular table facing towards the centre. Then the number of ways that can be done if A must have either E or F on his immediate right and E must have either F or D on his immediate right, is
MEDIUM
The number of four-letter words that can be formed with letters a, b, c such that all three letters occur is
EASY
The number of ways in which 3 prizes can be distributed to 4 children, so that no child gets all the three prizes, are
EASY
The sum of the digits in the unit's place of all the 4 - digit numbers formed by using the numbers 3, 4, 5 and 6, without repetition is :
MEDIUM
The number of permutations of the letters a1,a2,a3,a4,a5 in which the first letter a1 does not occupy the first position (from the left) and the second letter a2 does not occupy the second position (from the left) is
HARD
If all the seven letters of the word LEADING are permuted in all possible ways and the words thus formed are arranged as in the dictionary order, then the word in 2017th place is
EASY

If the number of all possible permutations of the letters of the word MATHEMATICS in which the repeated letters are not together is 90X, then X=

HARD
Five persons A, B, C, D and E are seated in a circular arrangement. If each of them is given a hat of one of the three colours red, blue and green, then the number of ways of distributing the hats such that the persons seated in adjacent seats get different coloured hats is
MEDIUM
The number of four-digit numbers strictly greater than 4321 that can be formed using the digit 0,1,2,3,4,5 (repetition of digits is allowed) is:
EASY
Ten different letters of an alphabet are given, words with five letters are formed from these given letters. Then, the number of words which have at least one letter repeated is
EASY
The total number of permutations of n(>1) different things taken not more than r at a time, when each thing may be repeated any number of times is
EASY
Letters in the word HULULULU are rearranged. The probability of all three L being together is
MEDIUM
5 boys of class VI6 boys of class VII and 7 boys of class VIII sit in a row. The number of ways they can sit so that boys of the same class sit together is
MEDIUM
The number of 4 letter words (with or without meaning) that can be formed from the eleven letters of the word EXAMINATION is
EASY
If P4n=20×P2n. Then, the value of n is
HARD
There are 10 red and 5 yellow roses of different sizes. If x is the number of garlands that can be formed with all these flowers so that no two yellow roses come together and y is the number of garlands formed with all these flowers so that all the red roses coming together, then 2x-y10!=
EASY
The number of 6 digit number that can be formed using the digits 0, 1, 2, 5, 7 and 9 which are divisible by 11 and no digit is repeated is:
MEDIUM
The number of ways in which 5 boys and 3 girls can be seated on a round table if a particular boy B1 and a particular girl G1 never sit adjacent to each other, is:
MEDIUM
Two girls and four boys are to be seated in a row in such a way that the girls do not sit together. In how many different ways can it be done?