38:38 I did not get what he meant. Y is a random variable indicating the time we have to wait. And for time, isn't it continuous? Then Y should also be a continuous RV. Why did he mention PMF rather than PDF?####[['Y', 'Mathematical_Related_Concept', 'NEU'], ['PMF', 'Mathematical_Related_Concept', 'NEU'], ['PDF', 'Mathematical_Related_Concept', 'NEU'], ['NULL', 'Instructor', 'NEU'], ['continuous RV', 'Mathematical_Related_Concept', 'NEU'], ['continuous', 'Mathematical_Related_Concept', 'NEU'], ['random variable', 'Mathematical_Related_Concept', 'NEU']]