Lol, if my student ever ask me why Hanako-san gave D-kun the most expensive gift, I would answer:
"It's because Hanako-san is dumb. She bought the presents to her most favorite friends first, but then only look at what is required of her, and thus forced to buy the most expensive gift to her least favorite person. Now, onto the next question."
It is blunt, since I'm calling Hanako-san an idiot. I could have replaced it with "no insight", but I'm teaching a 10 years old. At the very least, I managed to impart a wisdom to the student, which is to look ahead, and also take control of the flow of conversation in one fell swoop. Incidentally, it is also the best possible answer for a teacher. "Because it is math" just won't cut it for a curious kid.
She is trying to seduce me? Ha, try me, I will spoil all her suggestive attempts.