Question

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

Answer 1

15 litres of added water

Explanation:

We need to reduce 25% to 10%

Let the amount of acid in the mix be `x/100`

This gives a final acid content of `x/100xx25%`

The target concentration is 10%

Set `x/100xx25%=10%`

`x=(10%xx100)/(25%)`

`x=40`

Thus `40/100` of the final blend is the acid
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Let the total volume of the blend be `v`

We have 10 litres of acid so

`40/100v=10`

`v=(10xx100)/40 =100/4=25` litres all together

Thus the added water is 25-10=15 litres