Which of the following is irrational?

Which set is NOT closed under subtraction?

If $|S|=6$, then $|\mathcal{P}(S)|$ equals

If $|A|=4$ and $|B|=3$, then $|A\times B|$ equals

In a survey of $120$ students, $|P|=70$ like Python, $|R|=65$ like R, and $|P\cap R|=30$. How many like neither language?

The smallest set that contains the number $-7/3$ is

Which relation on $\mathbb{Z}$ is an equivalence relation?

On $X=\{1,2,3\}$, let $R=\{(1,1),(2,2),(3,3),(1,2),(2,3),(1,3)\}$. Then $R$ is

For all $n\ge 1$, let $S(n)=\sum_{k=1}^{n} k$. Which expression equals $S(n)$?

In a universe $U$ with $|U|=50$, if $|A|=20$, then $|A'|$ equals