A teller at a drive-up window at a bank had the following service times (in minutes) for 20 randomly selected customers:

SAMPLE
1	2	3	4
4.5	4.6	4.5	4.7
4.2	4.5	4.6	4.6
4.2	4.4	4.4	4.8
4.3	4.7	4.4	4.5
4.3	4.3	4.6	4.9

What are the 3-sigma control limits?

Select one:

a.

None of the other options.

b.

LCL = 4.212, UCL = 4.788

c.

LCL = 4.385, UCL = 4.615

d.LCL = 4.245, UCL = 4.755

e.

LCL = 4.414, UCL = 4.586