Q43 / 90 · JEE Main 2023 (31 Jan Shift 2) · Mathematics

The number of values of r∈p,q,~p,~q for which p∧q⇒r∨q∧(p∧r⇒q is a tautology, is :

  • A
    1
  • Correct answer
    B
    2
  • C
    4
  • D
    3

Solution

Given condition is, p∧q→r∨q∧p∧r→q).....(1)

We know conditional disjunction as,

p→q≡~p∨q

Hence, p∧r→q≡~p∧r∨q

Using De Morgan's law

p∧r→q≡~p∧r∨q≡~p∨~r∨q

Equation 1 can be written as,

⇒p∧q→r∨q∧~p∨~r∨q)

⇒~p∧q∨r∨q∧~p∨~r∨q)

⇒~p∨~q∨r∨q∧~p∨~r∨q)

⇒(~p∨~q∨r∨q∧~p∨~r∨q)

⇒~p∨t∧~p∨~r∨q)

⇒~p∨~r∨q

For above statement to be a tautology,

r can be ~p or q

When r=~p or r=q⇒~p∨~r∨q=t

∴ Two value of r are possible

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

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