The time needed for performing a machining operation is to be investigated. Historically, the process has had a standard deviation equal to 0.177 minutes. The means (in minutes) of 39 samples of n = 6 are:

Sample	Mean	Sample	Mean	Sample	Mean
1	3.78	14	3.74	27	3.80
2	3.75	15	3.77	28	3.68
3	3.69	16	3.88	29	3.90
4	3.80	17	3.70	30	3.54
5	3.91	18	3.81	31	3.74
6	3.78	19	3.70	32	3.88
7	3.98	20	3.83	33	3.66
8	3.88	21	3.82	34	3.62
9	3.96	22	3.81	35	3.50
10	3.90	23	3.72	36	3.64
11	3.95	24	3.71	37	3.98
12	3.95	25	3.98	38	3.84
13	3.90	26	3.89	39	3.79

The average of the 39 sample means is equal to 3.80.

a. Construct an xx -chart for this process with two-sigma limits. (Round the final answers to 2 decimal places.)

	UCL	LCL
Mean Control Limits

b. Is the process in control?

multiple choice

• Yes

• No