Aquality analyst wants to construct a control chart for determining whether three machines, all producing the same product, are under control with regard to a particular quality variable. accordingly, he sampled four units of output from each machine, with the following results:

machine measurements

#1 17 15 15 17

#2 16 25 18 25

#3 23 24 23 22

for upper and lower control limits of 23.29 and 16.71, which machine(s), if any, appear(s) to have an out-of-control process mean?

a.
machine #1

b.
machine #2

c.
machine #3

d.
all of the machines

e.
none of the machines