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.

We see that each member in the given set has the numerator one less than the denominator. Also, the numerator begin from $1$ and do not exceed $6 .$ Hence, in the set-builder form the given set is

$\left\{ {x:x = \frac{n}{{n + 1}},} \right.$ where $n$ is a natural number and $\left. {1 \le n \le 6} \right\}$

Write the following sets in roster form :

$\mathrm{E} =$ The set of all letters in the world $\mathrm{TRIGONOMETRY}$

Write down all the subsets of the following sets

$\{ a,b\} $

Which of the following are sets ? Justify your answer.

The collection of all natural numbers less than $100 .$

Consider the sets

$\phi, A=\{1,3\}, B=\{1,5,9\}, C=\{1,3,5,7,9\}$

Insert the symbol $\subset$ or $ \not\subset $ between each of the following pair of sets:

$\phi \,....\,B$

Let $A=\{1,2,3,4,5,6\} .$ Insert the appropriate symbol $\in$ or $\notin$ in the blank spaces:

$ 2 \, ....... \, A $