Abstract
Corporate social responsibility (CSR), as a concept that tackles economic, The introduction of private pension funds is the essence of the reform of the pension system in Serbia. Private pension funds in Serbia are based on voluntary benefits. Thus, the functioning of the pension system takes place in three interconnected processes: payments to a voluntary pension fund, investment of free funds, and ultimately programmed payments – pensions. The stability in the voluntary pension funds and the predictability of payments allow the quality of investment portfolio to be formed and achieve a long-term yield of investment. In this paper, we implement a well-known approximation method of Lagrange polynomial interpolation. We use it in order to find appropriate mathematical model for prediction of the number of fund members and the average salary in Serbia. This calculation is based on data (average salaries and fund member) from the last five years, i.e. from the period 2015-2019. We calculated the exact mathematical formula, then we compared the results and predictions obtained with that formula and with the formula from one of our previous works. In keeping with that, the appropriate conclusions were given..