Movies where something has to be solved in order to escape/survive?

Have seen:
Cube
Saw
Exam
Nine dead
House of nine
Fermat's room

I remember a slasher movie in the 80's with a scene in a school or college classroom. A male teacher is in the room with a classic "Train leaves the station" math problem on the chalkboard. The room has 2 doors with an answer on each one. The door with the correct answer will let the teacher live while the door with the wrong answer has the killer waiting with an ax. I can't remember the name of the movie though.

Open Grave 2013 is not bad

__________________
"Beliefs don't change facts. Facts, if you're rational, should change your beliefs" Ricky Gervais

Circle
Buried

A major chunk of Die Hard with a Vengeance has the conceit of the Bruce Willis and Samuel Jackson characters having to solve a series of riddles to stop bombs from going off.

__________________
"Film is a disease. When it infects your bloodstream it takes over as the number one hormone. It bosses the enzymes, directs the pineal gland, plays Iago to your psyche. As with heroin, the antidote to Film is more Film." - Frank Capra

There's Cube 2: Hypercube, but it's nowhere near as good as Cube.

There's the other Saw movies, but they're nowhere near as good as Saw, which is also nowhere near as good as Cube.

Maybe...
Sunshine (repairing a spaceship to escape the sun)
Dark Floors (figuring out a new dimension to escape a hospital)
Inception (implanting someone with an idea to escape a dream)

DO RECOMMEND.

DO NOT RECOMMEND.

Sphere.
The Stickup.
Dead and Buried.
The Serpent and the Rainbow.
Hellraiser.

Not a film, but worth mentioning the recent Doctor Who episode Heaven Sent.

If we're listing TV shows, I'd probably have to recommend nearly every episode of Star Trek and Stargate.