Answer:
There should be 125 litters of pure peroxide added to produce a new product that is 28% peroxide.
Step-by-step explanation:
The problem provides us with an equation we can use to find the concentration C of the new mixture, which is:

which will give us the concentration C as a decimal number.
We are interested in getting a concentration of 28%, which is written as 0.28 in decimal form. This is our C.
Now we can substitute it into the equation:

and now we can solve for x. We can start by multiplying both sides of the equation by (x+500) so we get:

Next, we can distribute dhe 0.28 on the left of the equation and we can also multiply the 0.1(500) on the right side, so we get:

so now we can subtract an x from both sides so we get:

which yields:

Now, we can subtract a 140 from both sides, so we get:

Which yields:

and finally we can divide both sides into -0.72 so we get:


So we need to add 125 litters of pure peroxide to produce a new product that is 28% peroxide.