Let $A=\{1,2,\{3,4\}, 5\} .$ Which of the following statements are incorrect and why ?
$1 \subset A$
Write the set $\{ x:x$ is a positive integer and ${x^2} < 40\} $ in the roster form.
Write the set $\left\{\frac{1}{2}, \frac{2}{3}, \frac{3}{4}, \frac{4}{5}, \frac{5}{6}, \frac{6}{7}\right\}$ in the set-builder form.
Which set is the subset of all given sets