Medium MCQ +4 / -1 PYQ · JEE Mains 2021

Let A = {2, 3, 4, 5, ....., 30} and '$\simeq$' be an equivalence relation on A $\times$ A, defined by (a, b) $\simeq$ (c, d), if and only if ad = bc. Then the number of ordered pairs which satisfy this equivalence relation with ordered pair (4, 3) is equal to :

  1. A 5
  2. B 6
  3. C 8
  4. D 7 Correct answer

Solution

ad = bc<br><br>(a, b) R (4, 3) $\Rightarrow$ 3a = 4b<br><br>a = ${4 \over 3}$b<br><br>b must be multiple of 3<br><br>b = {3, 6, 9 ..... 30}<br><br>(a, b) = {(4, 3), (8, 16), (12, 9), (16, 12), (20, 15), (24, 18), (28, 21)}<br><br>$\Rightarrow$ 7 ordered pair

About this question

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

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