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

MachineTotal Defectives

#1 23

#2 15

#3 29

#4 13

What is the estimate of the process proportion of defectives?

.08

.06

.04

.02

.01