You see a girl in your math class in the math lab and sit down next to her. She closes her math book. Currently, the class is working on chapter 4.5 and 4.6.You asked her what chapter she's on. She says she's looking over 4.5. Then a friend of yours who is also in the class joins the table. You and your friend start talking and the other girl is writing down some stuff. Your friend says to the girl, "Are you on Chapter 5 already?" The girl looks ashamed and said, "Yeah, I'm just, uh, reading it, though. How did you know?" Your friend said, "I saw you writing it down."
The girl told you that she's on 4.5, though. Why would she lie?