The library surveyed 240 people about their favorite movie. if 15% people chose documentaries, how many people chose documentaries

If the library surveyed 240 people and only 15% chose documentaries, then only 36 people chose documentaries and the other 204 chose something else other than documentaries. You had to get 15% into decimal form and to do that you move the "." in 15.0% left 2 places so you get 0.15. Then you multiply 240 by 0.15 and you get 36.