When walking home from school during the summer months, harold buys either an ice-cream or a drink from the corner shop. if harold bought an ice-cream the previous day, there is a 30% chance that he will buy a drink the next day. if he bought a drink the previous day, there is a 40% chance that he will buy an ice-cream the next day. on monday, harold bought an ice-cream. determine the probability that he buys an ice-cream on wednesday.