Question

How much pure water must be mixed with 10 liters of a 25% acid solution to reduce it to a 10% acid solution?


11 L
15 L
25 L

Answer 1

You don't mind a little algebra, do you? :)

Answer 2

Let's draw something...
But first, you should be used to treating percentages as what they really are: Fractions.
Or decimals.

25% is just 0.25
10% is just 0.10 or 0.1