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On the occasion if Deepawali festival, e...

On the occasion if Deepawali festival, each student in a class sends greeting cards to others. If there are 20 students in the class, find the total number of greeting cards exchanged by the students.

A

`""^(20)C_(2)`

B

`2.""^(20)C_(2)`

C

`2xx""^(20)P_(2)`

D

none of these

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The correct Answer is:
B
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OBJECTIVE RD SHARMA ENGLISH-PERMUTATIONS AND COMBINATIONS-Exercise
  1. The value of sum(r=0)^(m)""^(n+r)C(n) is equal to :

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  2. Every two persons shakes hands with each other in a party and the tot...

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  3. On the occasion if Deepawali festival, each student in a class sends g...

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  4. If ^n+2C8:^(n-2)P4: 57 : 16 , find ndot

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  5. Find the exponent of 3 in 100!

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  6. Ten different letters of an alphabet are given. Words with five letter...

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  7. If 7 points out of 12 are in the same straight line, then the number o...

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  8. about to only mathematics

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  9. No. of diagonals of a polygon are 170. No. of sides in this polygon ar...

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  10. The number of all possible selections of one or more questions from 10...

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  11. The number of ways of painting the faces of a cube with six diffe...

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  12. A box contains 4 white balls, 5 black balls and 2 red balls. The numbe...

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  13. Find the number of different permutations of the letters of the word ...

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  14. A person tries to form as many different parties as he can, out of his...

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  15. Find the number of ways in which 8 different flowered can be strung to...

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  16. The number of words which can be formed out of the letters a, b, c, d,...

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  17. The smallest value of x satisfying the inequality ""^(10)C(x-1)gt2.""^...

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  18. The number of arrangenments which can be made using all the letters of...

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  19. The number of ways of choosing a committee of 4 women and 5 men from 1...

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  20. A set contains 2n+1 elements. The number of subsets of this set conta...

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