What should be the volume of e-books

You can earn in the network on everything you just want. One way is the e-book . But in order to sell the book, you need to give it a presentation. It does not matter how many pages your book will consist of, the main thing is what is written there. Everybody thinks that first of all your book should have a volume of at least 100 pages. I can say with confidence that this opinion is very erroneous.