The three days of the Mathematical Modeling Competition happened to overlap with two University Physics classes.
Although it was an officially approved absence, Lu Zhou felt it would not look good to skip the very first class. He decided to deliver the leave slip himself rather than trouble the class monitor.
According to the schedule provided by the Academic Affairs Office, the University Physics instructor was Li Rongen, a highly experienced old professor. After getting his phone number from the school group chat, Lu Zhou called first to confirm that the professor was in his office before taking the leave slip over.
After knocking, Lu Zhou entered, placed the leave slip on the desk, and explained why he had come.
"Leave?" Professor Li glanced at the slip, took off his reading glasses, and looked up with a smile. "Your name is Lu Zhou, right?"
"Yes." Lu Zhou nodded.
Professor Li smiled. "All right. I'll give you two questions. If you solve one of them, I'll approve your leave slip."
There was such a thing?!
Lu Zhou was dumbfounded.
"What? Scared?" Li Rongen asked with a smile.
"No." Lu Zhou steadied himself and shook his head. "Please give me the questions, Professor."
"Here is the first one." Li Rongen flicked an A4 sheet into Lu Zhou's hand and watched him with a smile. "Write as much as you can. I want to see your work."
The question had already been prepared?!
Lu Zhou could not help feeling that this guy had planned it all along. Otherwise, how could he explain why the question had already been printed on an A4 sheet?
Even though he had guessed as much, Lu Zhou said nothing and picked up the sheet to read the question.
``` In a nuclear submarine, the half-life of U238 nuclei