Q14 / 87 · NTA Abhyas (JEE Main) 2020 · Mathematics · Functions

A function f: Z→Z is defined as fn=n+1n∈odd integern2n∈even integer. If k∈odd integer and fffk=33, then the sum of the digits of k is

  • A
    7
  • Correct answer
    B
    5
  • C
    9
  • D
    8

Solution

∵ k∈odd integer

fk=k+1 which is even

∴ffk=k+12

If k+12 is odd ⇒33=k+12+1⇒k=63 not possible (because k+12 is even)

If k+12 is even ⇒33=k+122⇒33=k+14⇒k=131

Sum of digits =5

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

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