It is true that the brain greatly outperforms the calculator, but it is apparent that humans make mistakes even with simple math problems, and take longer to answer, whilst the calculator just runs a bunch of bits through logic gates and pops out a correct result almost instantaneously.
Considering the above statement, it seems apparent that the human mind takes a completely different approach to arithmetic problems than the calculator.
Has there been any research that at least provides a general idea of the brain's approach?