## Elementary Algebra

Let X represent the amount of water to be added. After X is added, we obtain a 10% acid solution. A 40% acid solution has 60% water in it. A 10% acid solution has 90% water in it. We use the following guideline to solve this problem: Amount of water in original solution + Amount of water to be added = Amount of water in final solution. 60% $\times$ 50 + X = 90% $\times$ (50 + X) $.6 \times 50 +X = .9 \times (50+X)$ 30 + X = 45 + $\frac{9X}{10}$ $\frac{10X}{10}$ - $\frac{9X}{10}$ = 15 $\frac{X}{10}$ = 15 Multiply both sides by 10. X = 150 We must add 150 ml of distilled water.