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Original research
ECONOMIC EVALUATION OF TRACTOR USEFUL LIFE AS A DECISION-MAKING TOOL FOR AGRICULTURAL PRODUCTIVITY AND RURAL DEVELOPMENT IN SOUTH SUDANPages 141-150 Abstract
The objective of this study was to develop the mathematical model that can be used to predict the useful life for Sonalika DI-90 farm tractors in Juba. Data that sought the costs for spare parts, repairs, oils, oils and fuel filters, grease, tire replacement, fuel, and tractor operator, in addition to the annual operating hours and the purchase or list price were collected using well-structured questionnaires. The Microsoft Excel 2010 was used to perform regression analysis on the accumulated total cost per hour which was considered as a dependent variable and thus, labelled on Y-axis and the age of operation that was regarded as an independent variable and thus, labelled on Y-axis. The five models of exponential, linear, logarithmic, polynomial, and power were tried and it was determined that the polynomial model was the suitable model for predicting the useful life for the Sonalika DI-90 farm tractors operated in the two areas of Mapel and Rajaf East South of the Capital City of South Sudan Juba. The useful life for Sonalika DI-90 farm tractors was determined to be 18 years, with an accumulated operating hours of 4096.10 hours of operation.
Keywords: Farm Tractor, Juba City, Mathematical Model, Sonalika DI-90, South Sudan, Useful Life.
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Saman Nicola Wilba Nicola 
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