Startup Idea : Teaching online gaps

For student of programs like engineering, take us such a lot of time to understand tough theories and practice several mathematical problems. A website which can work as Youtube but just focused on summarizing videos which an user can use to explain a specific chapter of a book will help students save time and get the main ideas. Making it clearer, an user can make videos of the first chapters of a book and offer them for free, after that, the following chapter can be offer for a small amount of money. The idea is that each user is sure that the speaker has a good level of understanding the topic being discussed. Each speaker is ranked according to the users and get feedback about what people would like to learn and in what way.