Q20 / 54 · JEE Advanced 2017 (Paper 2) · Mathematics

Let S=1,2,3,….9. For k=1,2,…5, let Nk be the number of subsets of S, each containing five elements out of which exactly k are odd. Then N1+N2+N3+N4+N5=

  • A
    125
  • B
    252
  • C
    210
  • Correct answer
    D
    126

Solution

N1+N2+N3+N4+N5= Total ways – {when no odd}

Total ways =9C5

Number of ways when no odd, is zero     (∵ only available even are 2, 4, 6, 8)

∴ 9C5-zero=126

Hence, the correct answer is option: 'D'.

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