An automatic machine in a manufacturing process is operating accurately if the length
of an important subcomponent is normally distributed with a mean 80 cm and population
standard deviation of 2 cm
a)	Find the probability of length of one selected unit is less than 79 cm
b)	Find the probability of average length of 10 selected unit is less than 79 cm
c)	Find the probability of average length of 30 selected unit is less than 79 cm