Using Prepositions in English

Nick decided to set up an academy to teach what he did best. He placed the nad in a newspaper, and soon dozens of people signed up for his course. On the first day of the course, nick was delight but when the class started, the students started asking all kinds of questions related to using prepositions in english. Nick didn't understand what was going on. Finally, a student showed him the newspaper ad. It said, course on prepositions of value, 50 % discount, only this month. There was a typo in the ad. So it was all a misunderstanding.