Construction of Equation when working with mixture problems

Question

"Brine is a solution of salt and water. If a tub contains 50 gallons of a 5% solution of brine, how much water must evaporate to change it to an 8% solution? " Is the problem I'm working with but I'm having trouble understanding how to construct an equation can I get some help please? Do I use subtraction (0.08(50-x)) I'm really lost and help would be appreciated. Thank you

Answer 1

50(0.05) = 0.08(50-x)  x = gallons to be evaporated

 

5/2        = 4 - 0.08x

 

5/2 -4    = -0.08x

 

8/2- 5/2 = 0.08x

 

3/(2(.08)) = x = 18.75

Answer 2

I will leave my initial first paragraph up here so that the comment below makes sense. My understand of the characteristics of Brine are flawed. Mass is conserved but not volume. Thank you for clearing this up LeVar. 

 

Please follow Peters solution.

 

"You have 50 gallons of solution. 5% of the solution is salt and 95% is water. How much water must be separated and taken out of the solution so that there is 8% salt and 92% water. The amount of salt in the tub is constant throughout the whole question."