Question 254782
Let x pounds of coffee costing 3$ a pound should be mixed with 5 pounds of coffee costing $3.50 
The final mixture costs $3.25 a pound
Therefore we get,
           3x+5*(3.50) = (x+5)*(3.25)
           3x+ 17.5 = 3.25x+16.25
           3x-3.25x = 16.25-17.5
             -.25x  = -1.25
Multiplying by (-10), we get
               25x  = 125
                  x = 125/25
                  x = 5