Determination the mathematical model of repair and maintenance cost of New Holland TM155 and Valtra 8400 tractors in Markazi and Fars Provinces

Costs of repair and maintenance are most part of the cost of machinery usage. Cost estimation of repair and maintenance of agricultural machinery is very important for replacement and net return of management of machinery. This is an important factor to present a mathematical model for the cost predication of repair and maintenance. The main goal of research was to present a mathematical model of repair and maintenance cost modern tractors in selected province of Iran. In this case New Holland TM155 and Valtra 8400 tractors were selected in Markazi and Fars provinces. First of all a questionnaire including driver's information and technical data for the tractors was completed by randomly sampled tractor driver. In this case 100 questionnaires were distributed between users of each type of considered tractors during spring till summer of 2007. Provided data were analyzed by SPSS and Excel soft wares to do statistical analysis and determining appropriate mathematical models. T test was used to mean comparison of tractor’s cost and Z, F and R2 as statistical test and indexes were done to finding appropriate mathematical models. The average annual repair and maintenance costs of New Holland TM155 and Valtra 8400 were calculated 3304 and 3635 Ri/hr respectively. Results showed that the average repair and maintenance costs of Valtra 8400 were significantly higher than New Holland TM155 tractors at 5% confidence level. In this research appropriate mathematical models were offer to estimate repair and maintenance costs of each models.