The negation of $ \sim s \vee \left( { \sim r \wedge s} \right)$ is equivalent to

Which of the following is a contradiction

The statement $(p \Rightarrow q) \vee(p \Rightarrow r)$ is NOT equivalent to.

The Boolean expression $( p \Rightarrow q ) \wedge( q \Rightarrow \sim p )$ is equivalent to :

The contrapositive of the statement "If I reach the station in time, then I will catch the train" is 

Suppose $p, q, r$ are positive rational numbers such that $\sqrt{p}+\sqrt{q}+\sqrt{r}$ is also rational. Then