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?

If $x\in A$ and $A\in B$, then $x\in B$.

In the following, determine whether the statement is true or false. If it is true, prove it. If it is false, give an example.

If $A\subset B$ and $B\subset C$, then $A\subset C$

In each the following, determine whether the statement is true or false. If it is true, prove it. If it is false, give an example.

If $A\not\subset B$ and $\mathrm{B}\not\subset \mathrm{C}$, then $A\not\subset \mathrm{C}$

In the following, determine whether the statement is true or false. If it is true, prove it. If it is false, give an example.

If $x\in A$ and $A\not\subset B$, then $x\in B$

If $A\subset B$ and $x\notin B$, then $x\notin A$.