The mean service time $(\stackrel{}{x})$ of a physician is $25$ minutes with a standard deviation $()$ of $1$ minute. Upper specification limit $(USL)$ is $30$ minutes, whereas lower specification limit $(LSL)$ is $20$ for this process. What is the process capability ratio $(c_p)$ for this process? Is the process capable?

$Cp=1$; barely capable

$Cp=1\mathrm{.}5,$ capable

$Cp=1\mathrm{.}67,$ not capable

$Cp=1\mathrm{.}67,$ definitely capable

$Cp=1,$ not capable