During one semester at college I used to get a ride home with another guy from yeshiva. One evening he was having a test and asked if I could get a ride home from someone else in the class.
I answered that the only other frum people who live nearby are females and it will be yichud at that hour.
He (jokingly) told me that there is no issur of yichud with a girl taking calculus.
For some reason I decided to repeat this on a date and the girl just stared at me stone faced.
“You don’t find that funny?” I asked.
“Uh, I’m currently taking Calc II”.
Well, she ended up saying “no”, I can’t imagine why?