Bunuel wrote:

A 48 gallon solution of salt and water is 10% salt. How many gallons of water must be added to the solution in order to decrease the salt to 8% of the volume?

A. 8

B. 12

C. 13

D. 14

E. 16

Let x = amount of water to be added.

Water is 0% salt. It is added in on LHS to track on the idea that two quantities are being mixed (the 10% solution and water)**

(.10)(48) + 0x = (.08)(48 + x)

4.8 + 0x = 3.84 + .08x

.96 = .08x ---> 96 = 8x

x = 12

Answer B

**Method

Let 48 gallon solution = A

Let water to be added = B

A + B = Total volume of resultant solution

(A's Concentration)(A's Volume) + (B's Concentration)(B's Volume) = (Desired Concentration)(Total Volume of resultant solution)