Provide your best answer for the following math problem. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The problem is: milk contains 5 % water . what quantity of pure milk should be added to 10 litres of milk to reduce this 2 % ?
15 litres
4.54 litres.