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JEE Advanced2017MathematicsSets and RelationsActual

Let S = 1,2 , 3 , … . 9 . For k = 1,2 , … 5 , let N k be the number of subsets of S , each containing five elements out of which exactly k are odd. Then N 1 + N 2 + N 3 + N 4 + N 5 =

Options

  1. A125
  2. B252
  3. C210
  4. D126

Correct answer

D. 126

Step-by-step solution

N 1 + N 2 + N 3 + N 4 + N 5 = Total ways – when no odd Total ways = 9 C 5 Number of ways when no odd, is zero ( ∵ only available even are 2 ,   4 ,   6 ,   8 ) ∴   9 C 5 - zero = 126

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