Note: 1. Define events as and when required. 2. Rockwell hardness of pins of a certain type is known to have a mean value of Sill and a standard deviation ef 1.2. a} If the distribution is normal, what is the prebabilitg,r that the sample mean hardness for a random sample of 9 pins is at least 51? b} \"That is the [approximate] probability that the sample mean hardness for a random sample of 40 pins is at least 51