Pythagoras' theorem and quadratic equations are all in a day’s work for a humble teenager – who passed her maths GCSE six months early with almost full marks.

Xiaoyi Sun, a student at Hertswood Academy, Thrift Farm Lane, took the exam in November and thought it had gone “fairly well”.

But the 15-year-old could not mask her shock when her final mark of 94 per cent came back last week – one of the highest grades in the country.

She was one of a few pupils at the Borehamwood school selected to take the maths exam early and she is still reeling with excitement at her A* grade.

Xiaoyi, who lives in Borehamwood with her parents, said: “I have always enjoyed maths – I find numbers interesting and solving problems can be relaxing.

“I struggled to revise so when I found out my mark my reaction was ‘wow’. I would still love to improve my final mark one day, because I missed out on stupid points.

“My parents were very proud of me though.”

The keen pianist has been considering following in her parent’s footsteps to become a doctor, but admits she is unsure what the future holds.

Despite her impressive achievement, she remains modest about her school-work and is quick to point out others who are just as bright.

She added: “I like talking to people about maths. I revised for the exam with my friend and I found that interesting and useful.

“I am looking forward to my future now.”