set A has an expected return of $20\%$ and a standard deviation of $25\%.$ The risk$-$free rate is $10\%.$ What is the reward$-$to$-$variability ratio?

Multiple Choice

$0\mathrm{.}40$

$0\mathrm{.}50$

$0\mathrm{.}75$

$0\mathrm{.}80$