Lets call x the amount of 18% solution and y the amount of 40% solution, and write as equations the info of the problem: 18x + 40y = 10(20) x + y = 10 lets multiply the second equation by -18 and add to the first: 18x + 40y = 200 -18x -<span> 18y = -180 </span>---------------------- 0 + 22y = 20 y = 20/22 = 10/11 and substitute in the original equation: x <span>+ y = 10 </span>x = 10 - y x = 10 - 10/11 x = 110/11 - 10/11 x = 100/11 so they have to use 100/11 liters of 18% solution and 10/11 liters of 40% solution
