There are an estimated 327 million people in the United States, according to the U.S. Census Bureau, and perhaps you have wondered: How many of them are in "Avengers: Infinity War"? Fifteen percent? Thirty-four percent? Spoiler: Nobody knows for certain how many people appear in "Avengers: Infinity War," opening Friday. It's a mystery. The Marvel Studios and IMDB cast lists indicate about 80 cast members – some playing Iron Man and Spider-Man, some playing Man on Bus.