Identify the highest possible threshold for accepting all genuine requests in a biometric authentication system where imposter attempts generate values between $0$ and $0\mathrm{.}5$ and genuine attempts generate values between $0\mathrm{.}3$ and $1.$

$0\mathrm{.}3$

$1\mathrm{.}0$

$0\mathrm{.}5$

$0\mathrm{.}8$