Question 98306
 
Let x=amount of water that needs to be added

Now we know that the amount of pure acid in the 25% solution (0.25(50)) plus the amount of pure acid in the water that's added (0) has to equal the amount of pure acid in the final mixture (0.10(50+x)).  So our equation to solve is:

0.25*50=0.10(50+x)  get rid of parens

12.5=5+0.10x  subtract 5 from both sides

12.5-5=5-5+0.10x  combine like terms

7.5=0.10x  divide both sides by 0.10

x=75 ml------------------------------amount of water needed

CK
0.25*50=0.10*125
12.5=12.5

Hope thsi helps---ptaylor