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

`.^(n)C_(r)+2.^(n)C_(r-1)+.^(n)C_(r-2)=`

A

`2.^(n)C_(r+2)`

B

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

C

`.^(n+2)C_(r+2)`

D

None of these

Text Solution

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The correct Answer is:
c
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FIITJEE-PERMUTATIONS & COMBINATIONS-ASSIGNMENT PROBLEMS (OBJECTIVE) LEVEL I
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  2. On a railway there are 20 stations. The number of different tickets re...

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  3. .^(n)C(r)+2.^(n)C(r-1)+.^(n)C(r-2)=

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  4. How many different nine digit numbers can be formed from the numebr 22...

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  9. The number of permutations of the letters a,b,c,d,e,f,g such that neit...

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  12. The number of numbers less than 1000 than can be formed out of the dig...

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  14. The sum of digits in the units place of all numbers formed with the...

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  15. Two numbers are chosen from 1,3,5,7,…147, 149 and 151 multiplied toget...

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  17. Let A={x(1),x(2),x(3)....,x(7)},B={y(1)y(2)y(3)}. The total number of ...

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  18. Q) The number ofpositive integer pairs (x, y) such that 1/x+1/y=1/2007...

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  19. The total number of positive integral solution of 15<x1+x2+x3lt=20 is ...

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