21.
Let $$p$$ and $$q$$ be any two logical statements and $$r:p \to \left( { \sim p \vee q} \right).$$ If $$r$$ has a truth value $$F,$$ then the truth values of $$p$$ and $$q$$ are respectively :
$$p \to \left( { \sim p \vee q} \right)$$ has truth value $$F.$$
It means $$p \to \left( { \sim p \vee q} \right)$$ is false.
It means $$p$$ is true and $${ \sim p \vee q}$$ is false.
$$ \Rightarrow p$$ is true and both $$\sim p$$ and $$q$$ are false.
$$ \Rightarrow p$$ is true and $$q$$ is false.
22.
Consider the following statements
$$P$$ : Suman is brilliant
$$Q$$ : Suman is rich
$$R$$ : Suman is honest
The negation of the statement “Suman is brilliant and dishonest if and only if Suman is rich” can be expressed as
Suman is brilliant and dishonest if and only if Suman is rich is expressed as
$$Q \leftrightarrow \left( {P \wedge \sim R} \right)$$
Negation of it will be $$ \sim \left( {Q \leftrightarrow \left( {P \wedge \sim R} \right)} \right)$$
23.
Negation of the conditional : “If it rains, I shall go to school” is
$$p :$$ It rains, $$q :$$ I shall go to school
Thus, we have $$p \Rightarrow q$$
Its negation is $$ \sim \left( {p \Rightarrow q} \right){\text{i}}{\text{.e}}{\text{., }}p \wedge \sim q$$
i.e., It is rains and I shall not go to school.
24.
In the truth table for the statement $$\left( {p \to q} \right) \leftrightarrow \left( { \sim p \vee q} \right),$$ the last column has the truth value in the following order is
We observe the columns for $$ \sim \left( {p \leftrightarrow \sim q} \right)$$ and $${p \leftrightarrow q}$$ are identical, therefore
$$ \sim \left( {p \leftrightarrow \sim q} \right)$$ is equivalent to $${p \leftrightarrow q}$$
But $$ \sim \left( {p \leftrightarrow \sim q} \right)$$ is not a tautology as all entries in its column are not $$T.$$
27.
For any two statements $$p$$ and $$q,$$ the negation of the expression $${p \vee \left( { \sim p \wedge q} \right)}$$ is:
$$p :$$ A number is a prime
$$q :$$ It is odd.
We have, $$p \Rightarrow q$$
The inverse of $$p \Rightarrow q{\text{ is }}\sim p \Rightarrow \sim q$$
i.e., if a number is not a prime then it is not odd.
29.
If the Boolean expression $$\left( {p \oplus q} \right) \wedge \left( { \sim p \odot q} \right)$$ is equivalent to $$p \wedge q,$$ where $$ \oplus , \odot \in \left\{ { \wedge , \vee } \right\}$$ then the ordered pair $$\left( { \oplus , \odot } \right)$$ is: