2.3 BP petrol is to be stocked in a bulk tank once at the beginning of each week and then sold to individual customers. Consider the joint density of Y1, the proportion of the capacity of the tank that is stocked at the beginning of the week and Y2, the proportion of the capacity sold during the week, given by 0 5 3'2 5 3'1 5 1' elsewhere. f(y1:y2) = {0?}'1. In each week an average of 700/0 of the petrol is sold and an average of 30% of the petrol remains in the Caltex bulk tank at the end of each week. In an},r given week of the year= what is the probability that the amount of petrol sold during the week is more than the amount of petrol that was stocked in the beginning of the week? (2)