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If ""^(n)P(7)=42. ""^(n)P(5). find n....

If `""^(n)P_(7)=42. ""^(n)P_(5).` find n.

A

5

B

7

C

12

D

9

Text Solution

Verified by Experts

The correct Answer is:
C
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AAKASH SERIES-PERMUTATIONS & COMBINATIONS-EXERCISE-I
  1. If ""^(8)P(r)=""^(8)P(r+1) then r is

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  2. If ""^(n)P(7)=42. ""^(n)P(5). find n.

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  3. IF ""^(12)P(r )=""^(11)P(6)+6^(11)P5, then r=

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  4. If ""^(n)P(4)=1680, find n.

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  5. The number of different signals that can be made by 5 flags from 8 fla...

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  6. A man has 4 sons and there are 5 schools within his reach. In how many...

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  7. The number of 3 digit numbers using 1, 2, 3, 4, 5 if no digit is to be...

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  8. Using the digits 0,2,4,6,8 not more than once in any number ...

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  9. Number of permutations that can be made using all the letters of the w...

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  10. Number of 4 letter permutations that can be made from the letters of t...

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  11. The number of arrangements that can be formed by taking all the ...

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  12. The letters of the word “ARTICLE” are taken four at a time and arrange...

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  13. The number of arrangements which can be made out of the letters of the...

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  14. 10 men and 6 women are to seated in a row so that no two wowe...

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  15. the number of 3 digited numbers that can be formed that can ...

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  16. The number of 4 letter words than can be formed using the lett...

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  17. Eight different letters of an alphabet are given . Words of f...

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  18. A letter lock consists of three rings each marked with 5 different let...

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  19. Find the the number of functions from a set A containing 5 elements in...

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  20. The number of injections from Set - A containing 5 elements to a Set -...

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