In rule method the null set is represented by
Let $A=\{1,2,\{3,4\}, 5\} .$ Which of the following statements are incorrect and why ?
$\{ 3,4\} \in A$
Show that the set of letters needed to spell $"\mathrm{CATARACT}"$ and the set of letters needed to spell $"\mathrm{TRACT}"$ are equal.
State whether each of the following set is finite or infinite :
The set of animals living on the earth
Examine whether the following statements are true or false :
$\{ a\} \in \{ a,b,c\} $