In a committee,$50$ people speak French,$20$ speak Spanish and $10$ speak both Spanish and French. How many speak at least one of these two languages?

In a school,$20$ teachers teach either Mathematics or Physics. If $12$ teachers teach Mathematics and $4$ teachers teach both subjects,then the number of teachers teaching only Physics is:

If $X$ and $Y$ are two sets such that $n(X) = 17$,$n(Y) = 23$ and $n(X \cup Y) = 38$,find $n(X \cap Y)$.

The number of $4$-digit numbers which are neither a multiple of $7$ nor a multiple of $3$ is ..... .

In a city,$20\%$ of the population travels by car,$50\%$ travels by bus,and $10\%$ travels by both car and bus. Then,the percentage of persons travelling by car or bus is......$\%$

Let $S = \{1, 2, 3, 5, 7, 10, 11\}$. The number of nonempty subsets of $S$ such that the sum of all elements is a multiple of $3$ is $........$