A manufacturer embarking on a Six Sigma program sets the goal of having true six$-$sigma capability for all processes by the end of the month. If their current process capability index on a key metric is less than $2\mathrm{.}0$ and the process capability ratio is $1\mathrm{.}5,$ what must happen with the process standard deviation?

The process standard deviation must be reduced by $25\%.$

The process standard deviation must be reduced by $33\%.$

The process standard deviation must be reduced by $50\%.$

The process standard deviation must be reduced by $67\%.$