The probability of Type I error is the likelihood of finding a mean outside
the safe zone for the 4 pools.
In hypothesis testing, a Type I error is the error of rejecting a true null
hypothesis.
From a similar question, the possible parameters are;
The safe pH levels for swimming pools is between 7.2 and 7.8
The standard deviation is 0.2
The probability that the pH is within the safe zone is found as follows;
[tex]The \ z-score, \ Z = \mathbf{\dfrac{\overline x - \mu}{\dfrac{\sigma}{n} }}[/tex]
Which gives;
[tex]\mathbf{P \left(\dfrac{7.2 - 7.5}{\dfrac{0.2}{\sqrt{4} } } < \dfrac{\overline x - \mu}{\sigma} < \dfrac{7.8 - 7.5}{\dfrac{0.2}{\sqrt{4} }} \right)} = P(-3 < Z < 3)[/tex]
P(-3 < Z < 3) = P(Z < 3) - P(Z > -3) = P(Z < 3) - (1 - P(Z < 3))
P(Z < 3) - (1 - P(Z < 3) = 2·P(Z < 3) - 1
2·P(Z < 3) - 1 = 2 × 0.9987 - 1 = 0.9974
The probability that the swimming pool is not safe = 1 - (2·P(Z < 3) - 1)
1 - (2·P(Z < 3) - 1) = 1 - 0.9974 = 0.0026
Which gives;
Learn more about hypothesis testing here:
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