If a 7% saline solution and a 4% saline solution are mixed to make 500 milliliters of a 5% saline solution, how much of each solution, to the nearest milliliter, is needed?

 The answer is 167 milliliters of 7% solution and 333 milliliters of 4% solution x + y = 500 x = 500 - y 0.07x + 0.04y = 25 (substitute 500 - y for x) 0.07(500 - y) + 0.04y = 25 35 - 0.07y + 0.04y = 25 -0.03y + 35 = 25 -0.03y = -10 y = 333.333... y [ = about 333 x = 500 - y = 500 - 333 = 167 hope it helps