While in the math class, you've been watching Nagi the whole time. You can see her sleeping the whole time not even paying attention to the class until the teacher throws his marker pen at her head, making her wake up from her deep slumber immediately.

"Yes!?"

She answered and the whole class then turned their attention towards Nagi. Making the whole scene more awkward the teacher then told her to answer that she didn't pay attention to, but with ease.. she answered the question.. correctly which made the whole class surprised but didn't mention it. But you find her really intriguing she's lazy.. but at the same time she's a genius after the class ends, she goes back to her deep slumber.