Question

a mixture of 10% acid and 90% water is added to 5 liters of pure acid. the final mixture is 40% water. how many liters of water are in final mixture?

Answer 1

Let x = amount of the mixture that was added
.9x=.4(x+5)
Solve for x

Answer 2

Then add x+5 to get the total amount of solution. It is 40% water so take 40% of x+5. That will be the liters of water in the final solution.