Write the following sets in roster form :
$\mathrm{F} =$ The set of all letters in the word $\mathrm{BETTER}$
Write the following intervals in set-builder form :
$\left[ {6,12} \right]$
Examine whether the following statements are true or false :
$\{ 1,2,3\} \subset \{ 1,3,5\} $
State whether each of the following set is finite or infinite :
The set of letters in the English alphabet
Let $A=\{1,2,\{3,4\}, 5\} .$ Which of the following statements are incorrect and why ?
$\varnothing \in A$