Medium MCQ +4 / -1 PYQ · JEE Mains 2022

Let a function f : N $\to$ N be defined by

$$f(n) = \left[ {\matrix{ {2n,} & {n = 2,4,6,8,......} \cr {n - 1,} & {n = 3,7,11,15,......} \cr {{{n + 1} \over 2},} & {n = 1,5,9,13,......} \cr } } \right.$$

then, f is

  1. A one-one but not onto
  2. B onto but not one-one
  3. C neither one-one nor onto
  4. D one-one and onto Correct answer

Solution

<p>When n = 1, 5, 9, 13 then ${{n + 1} \over 2}$ will give all odd numbers.</p> <p>When n = 3, 7, 11, 15 .....</p> <p>n $-$ 1 will be even but not divisible by 4</p> <p>When n = 2, 4, 6, 8 .....</p> <p>Then 2n will give all multiples of 4</p> <p>So range will be N.</p> <p>And no two values of n give same y, so function is one-one and onto.</p>

About this question

Subject: Mathematics · Chapter: Sets, Relations and Functions · Topic: Sets and Operations

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