The aim of this study is to compare the ways individuals who got formal mathematics education and the ones who didn’t get follow while calculating from the mind. The study was carried out by sampling a total number of 12 people 6 of whom were people who got formal mathematics education and 6 of whom were people who are illiterate and learnt to do mathematical operations through informal methods. The data was collected through an interview form which included several questions evaluating the four operations skills. In the study in which descriptive analysis method was used, it was observed that both the individuals who got formal education and the ones who didn’t get applied to similar strategies like grouping, taking multiples, rounding to decimals and operating over mold numbers in questions which require addition and subtraction operations. But partial differences were determined in the mental calculation methods in the questions which require multiplication and division operations. It was defined that the individuals who didn’t get formal education obtained their calculating skills as a result of dealing with daily routines which require calculation at large and that they naturally benefit from the decimal system and its operational features while doing the calculations.