A quality analyst wants to construct a control chart for determining whether four machines, all producing the same product, are in control with regard to a particular quality attribute. Accordingly, she inspected $1,000$ units of output from each machine in random samples, with the following results:

Machine Total Defectives

#$123$

#$215$

#$329$

#$413$

What is the estimate of the process proportion of defectives?

$\mathrm{.}02$

$\mathrm{.}06$

$\mathrm{.}04$

$\mathrm{.}01$

$\mathrm{.}08$