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""^(n-2)C(r)+2.""^(n-2)C(r-1)+""^(n-2)C(...

`""^(n-2)C_(r)+2.""^(n-2)C_(r-1)+""^(n-2)C_(r-2)` is equal to

A

`""^(n+1)C_(r)`

B

`""^(n)C_(r)`

C

`""^(n)C_(r+1)`

D

`""^(n-1)C_(r)`

Text Solution

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The correct Answer is:
B
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AAKASH SERIES-PERMUTATIONS & COMBINATIONS-PRACTICE EXERCISE
  1. If ""^(35)C(n+7)=""^(35)C(4n-2), then all the values of n are given by

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  2. IF ""^(15)C(r+3)=""^(15)C(2r-3), then r=

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  3. ""^(n-2)C(r)+2.""^(n-2)C(r-1)+""^(n-2)C(r-2) is equal to

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  4. If ""^(18)C(r)=""^(18)C(r+2) then ""^(R )C(5)=

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  5. If ""^(n)C(4)=""^(n)C(8), then ""^(n)C(2) is

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  6. ""^(29)C(5)+sum(r=0)^(4)""^((33-r))C(4)=

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  7. ""^(15)C(8)+""^(15)C(9)-""^(15)C(6)-""^(15)C(7) is equal to

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  8. If ""^(18)C(15)+2(""^(18)C(16))"+"^(17)C(16)+1=""^(n)C(3) then n is

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  9. ""^(14)C(4)+sum(j=1)^(4)""^((18-j))C(3) is equal to

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  10. If p and q are the greatest values of ""^(2n)C(r) and ""^(2n-1)C(r) re...

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  11. If ""^(n+1)C(3)=4(""^(n)C(2)), then n is equal to

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  12. ""^(2n)C(2)-2""^(n)C(2)=

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  13. The least positive integral value of x which satisfies the inequality ...

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  14. The least value of the natural numbar 'n' satisfying C(n,5)+C(n,6)gtC(...

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  15. If ""^(n)C(r-1):""^(n)C(r):""^(n)C(r+1)=2:4:5 then (n,r) is

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  16. ""^(n) C(r-1) = 330 ,""^(n)C(r)=462 , ""^(n)C(r+1) = 462 implies r=

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  17. ""^(37)C(4)+sum(r=1)^(5)(42-r)(C(r))=

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  18. The number of ways that 3 English, 3 Hindi & 3 Telugu books can be cho...

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  19. The number of ways can 5 red and 4 white balls be drawn from a bag con...

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  20. Every body in a room shakes hands with every body else. The total numb...

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