Simulates a given number of
trucks, with loads of a random number of bags
in the given (closed) interval.
Each bag has a Gaussian weight, with parameters μ and
σ, such as for customers' trucks leaving a factory in
a certain period, say, one month.
The final results may include (or not) a column
(1..trucks) to enumerate each truck and give its
average bag weight. For use elsewhere, these columns
my be inappropriate.
Draws a graph of averages
and truck loads (number of bags). | 
