A fertilizer spreading machine is set to spread 75 tons of fertilizer in each and every plot of land. The actual weights of fertilizer spread onto each plot of land are normally distributed with the mean 75 tons and standard deviation 0.8 tons.
a) Determine the probability that 20 plots chosen at random will have a mean fertilizer weight of 74.5 tons or more?
b) Determine the probability that a single plot selected at random will have a load weighing 74.5 tons or more?