300 Optimization of Linear Mathematical Models Problem 4 An aggregate mixture contains a minimum of 30 percent sand and no more than 60 percent gravel nor 10 percent silt. Three sources of aggregate are available. Determine the mix of minimum unit cost, $/yd3 (a) Formulate a minimum cost model. Define all control variables with proper unit measures. (b) Write in the standard form of linear programming. Define slack and surplus control variables and their units