Harold used a 3% iodine solution and a 20% iodine solution to make a 95- ounce solution in which was 19% iodine. How many ounces of the 3% iodine solution did he use?

Let x = the amount of 3% iodine solution. Let y = the amount of 20% iodine solution. Because the total amount of solution was 85 oz., then x + y = 85. The amount of each kind of solution added together and set equal to the amount of 19% solution could be expressed in the equation 0.03x + 0.20y = 0.19(85); Use both equations to solve for x. Multiply the second equation by 100 to remove the decimal point: 3x + 20y = 19(85). Simplify that equation: 3x + 20y = 1805. Multiply the ?rst equation by -20: -20x + -20y = -1700. Add the two equations to eliminate y: -17x + 0y = -85. Divide both sides of the equation by -17: -17x/-17 -85/-17 = x = 5. The amount of 3% iodine solution is 5 ounces.