The diameter of a rivet manufactured by a certain process has a mean Ux=50mm and a standard deviation Zx=0.45mm. The largest possible value for the probability that the diameter of the rivet is outside the interval 49.1 to 50.9mm is 0.25 .
i. Explain what the result means to the ordinary person?

ii. Which theory would you recommend for solving the above problem and give your reason(s).