You get paid what you want. Period.
While deciding the price of the book, we ask you how much you’d like to earn per sale (in other words, what royalty you’d like to earn). If you decide you’d like to earn Rs. 10/- per sale, that is exactly what you will earn after each sale.
There are no complicated formulae, no percentages, no revenue sharing, nothing.
You get paid what you want.
Here’s a blog on the topic.