Question

How much water must be added to 20 L of a 10% solution of boric acid to reduce it to a 4% solution?

Answer 1

You have to add 30 litres of water

Explanation:

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:

`2/(20+x)=4/100`

The equation comes from the fact that the amount of acid is unchanged (2L) and the sum of water and acid is increased by `x` (added water)

`2/(20+x)=2/50`

`40+2x=100`

`2x=100-40`
`2x=60`
`x=30`