How much water must be added to 20 L of a 10% solution of boric acid to reduce it to a 4% solution?
You have to add 30 litres of water
At the beginning you have 20 L of 10% solution, so it consists of 2L of acid and 18 L of water.
Now you have to calculate the amount of water to add to change the solution to 4%.
To do this you have to solve equation:
The equation comes from the fact that the amount of acid is unchanged (2L) and the sum of water and acid is increased by