IN versus ON

[nordway]

Are both sentences correct?
I could not do one problem IN the exam.
I could not do one problem ON the exam.
If both prepositions are OK, which one is more common here?

[bhaisahab]

Are both sentences correct?
I could not do one problem IN the exam.
I could not do one problem ON the exam.
If both prepositions are OK, which one is more common here?

I'd use "in".

[Chicken Sandwich]

NOT A TEACHER

I think that "on" is acceptable in AmE, see this thread.