Concrete blocks to be used in a certain application are supposed to have a mean compressive strength of 1500 MPa. Samples of size 1 are used for quality control. The compressive strengths of the last 40 samples are given in the following table.

Previous results suggest that a value of σ = 15 is reasonable for this process.
a. Using the value 1500 for the target mean μ, and the values k = 0.5 and h = 4, construct a CUSUM chart.
b. Is the process mean in control? If not, when is it first detected to be out of control?

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