What is the contrapositive of this simple proposition? 
If $a$ and $b$ are rational then $ab$ and $a+b$ are also rational.

What is the contrapositive of this proposition?


*

*If $ab$ and $a+b$ are not rational then $a$ and $b$ are not rational.

*If $ab$ or $a+b$ are not rational then $a$ or $b$ are not rational.

Your statement: $a$ and $b$ rational $\implies$ ($ab$ and $a+b$) rational.
Contrapositive: not ($a+b$ and $ab$ rational) $\equiv$ not ($a+b$ rational) or not ($ab$ rational) $\implies$ not($a$ and $b$ rational) $\equiv$ not ($a$ rational) or not ($b$ rational).
(My initial answer had a silly mistake in it)
