These patients often have significant damage to the prefrontal areas of their brain, which can cause trouble with mental operations, operations that need to be carried out successively, backward operations, and numerical problems that require multiple steps. In these individuals written mathematical problem solving is easier to do than mental math operations.
Prefrontal lobes. (www.cast.org)
There a 3 different types of difficulties that lead to problems in frontal acalculics.
These difficulties lead to trouble maintaining the conditions of the tasks and impulsiveness in answers (due to attention difficulties) and ultimately the incorrect answer (due to perseveration). Also, these individuals have trouble analyzing the conditions of calculations and in turn are unable to develop and algorithm for the solution. It is important to note that elementary arithmetic is generally preserved to some extent, it is in more complex numerical problems that problems arise.