Instead of one observation outside of 3 from the mean as in Exercise 17, suppose a quality

Instead of one observation outside of 3σ from the mean as in Exercise 17, suppose a quality control engineer decides to use only the run chart rule that the system is out of control if 8 observations in a row lie on the same side of the mean. What is the probability that this would happen based on random chance variation alone? What assumptions do you have to make to answer this?