The biographical sketch of Rabbi Moshe Feinstein that appears in Igrot Moshe volume 8 describes the following (my translation):
The Communist takeover meant the schools taught against religion. Some of the older Jewish students would argue back, citing teachings of their rabbi [Moshe Feinstein]. One infuriated teacher (herself Jewish) finally replied, "What does that rabbi of yours know, if he can't solve this calculus problem?!"
Eventually the problem was brought to Rabbi Feinstein; who requested a calculus textbook, read it, and then solved it.
Have any details about this story (other than the ones printed there) survived to this day?