For some reason, people with no conceivable financial stake in the answers are fascinated with the box office grosses of new motion pictures. I was once in a sports bar near the airport in Hartford, Connecticut — don't ask why I was there; I don't even drink — and one of the lady bartenders asked me what I did for a living. When I said I was a TV writer, she said, "So, how do you think the new Bruce Willis pic will do this weekend?" Though I said I had no idea and that I didn't even know there was a new Bruce Willis movie opening, she persisted in discussing it with an interest that probably exceeded Bruce's.
So in case she's reading this: Here's an article about how the early grosses are tallied for press releases. The process is sloppy but most people accept it as accurate. It's kind of like the way we choose our presidents.