'Students are serious'is false statement then
its negation 'students are not serious' must
be a true statement.
Now, equivalent proposition of 'students are not serious' is 'All students are not serious' and also 'some students are not serious' can be true statements.
Now, equivalent proposition of 'students are not serious' is 'All students are not serious' and also 'some students are not serious' can be true statements.


