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# math Question ( Percentages / Diluent )?

How many mL of water should be added to 480mL of 70% solution to prepare a 30% solution?

How do you go about doing this I completely forgot?

It's not 4!

Haha.

I know the answer, I just don't know how to do it...

### 2 Answers

- Anonymous8 years agoFavorite Answer
If you have 480mL of 70% solution, this means that 70% of 480mL is the solute and the rest (30%) is the solvent (water). How much solute is there? Perform this calculation to find out.

(70*480)/100 = 7*48 = 346g

This is important because we want 346 to be 30% of our final solution. If it is, how much final solution is there? If we let x represent the unknown amount of the final solution then

346/x = 30/100.

We can multiply both sides by 100, divide both sides by 30 and multiply both sides by x to get

346 * 100 / 30 = x.

You calculate this with a machine if you can't do it by hand to get

x = (1153 + 1/3) mL = 1153.3333... mL

Now, that is the final amount of solution and you already have 480mL so you still need

(1153.3333.... - 480)mL = 673.333... mL

of water.