A gasoline wholesale distributor has bulk storage tanks that hold fixed supplies and
are filled every Monday. Of interest to the wholesaler is the proportion of this supply
that is sold during the week. Over many weeks of observation, the distributor found
that this proportion could be modeled by a beta distribution with α = 4 and β = 2.
Find the probability that the wholesaler will sell at least 90% of her stock in a given
week.