The diameter of ball-bearings produced by a machine is a random variable having a normal distribution with mean 6.00mm and standard deviation 0.02 mm. If the diameter tolerance is ;1%, find the proportion of ball-bearings produced that are out of tolerance. After several years’ use, machine wear has the effect of increasing the standard deviation, although the mean diameter remains constant. The manufacturer decides to replace the machine when 2% of its output is out of tolerance. What is the standard deviation when this happens?