The extremist -- who dropped out of the prestigious Olso Handelsgymnasium aged 17 before picking up his leaving diploma -- has spent this summer cramming mathematics ahead of the exam later this year, Vibeke Hein Bæra told Norway's Dagbladet.
The killer caused a furore at the end of last month when it emerged that he had applied to study political science at the University of Oslo, with Norway's education minister going so far as to consider changing the law to prevent him.
During Breivik's trial last year, one of the killer's former friends spoke about how his lack of high-school or university qualifications had made him fall further and further behind his peers, arguing that this was one of the underlying motivations for his attacks.
In his manifesto, Breivik claimed to have spent 16,320 hours studying on-line, giving him "an informal education consisting of the equivalent of eight university years (or equivalent to two bachelor degrees and one master degree)."
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Breivik killed 77 people and wounded 242 others when he detonated a bomb in central Oslo and then opened fire at a Labour party youth camp in July 2011.