The amount of kerosene, in thousands of liters, in the tank at the beginning of any day is random amount Y from which random amount X is sold throughout that day. Assume that the tank isn't resupplied throughout the day so that x ? y, and suppose that the joint density function of these variables is f(x,y) = 2 for 0 < x < y < 1. Determine the that the amount of kerosene sold is between 0.25 and 0.50 thousands liters given that amount in tank at the start of the day is 0.90 thousands liters. (Hint: f(x|y) = f(x,y) / fy(y) ).