According to most psychologists who specialise in dreams, the Unconscious is a symbolic processor. It's not the literal meaning of the content but the symbolic or representational meaning that needs to be uncovered. That meaning lurks in the Unconscious, so it's not directly accessible - if it were it wouldn't be unconscious. It is common cause amongst psychologists (my wife is a ClinPsych) that what pops into the conscious is a disguised and symbolic representation of what's really going on in the Unconscious.
For that reason it's very unlikely that the recurring maths exam dream has anything to do with a maths exam. Rather, as is normal, you have some or other unresolved issue/s, and your brain is testing and trying pathways and mechanisms to resolve & integrate those conflicts by modelling along paths it had previously used (such as your ancient maths exam). What the symbolic representation of the maths exam actually means can be very individual, and that can take a while under expert guidance to uncover.