A tank holds x gallons of a saltwater solution that is 20% salt by volume. One Fourth of the water is evaporated, leaving all of the salt. When 7 Gallons of water and 14 gallons of salt are added, the resulting mixture is 33 1/3 % salt by volume. What is the value of x? Choose the correct choice.
A) 37.5  B) 75  C) 105  D) 150  E) 175
Nope, 150. I can only get it by following PR's backsolving explanation. I hate that.   Original mixture has 20% salt and 80% water.   Total = x   Out of which Salt = 0.2x and water = 0.8x   Now, 1/4 water evaporates and all salt remains.   So what remains is 0.2x salt and 0.6x water.   Now 14 gallons salt is added and 7 gallons of water is added.   So salt now becomes -&gt; (0.2x + 14) and water --&gt; (0.6x+7)   Amount of salt is 33.33% of total. So amount of water is 66.66%. So salt is half of the volume of water.   So (0.2x+14) = (0.6x+7)/2 = &gt; 0.2x = 21   Solving, x = 105   Answer : 105
<result>C</result>
A tank holds x gallons of a saltwater solution that is 20% salt by volume. One Fourth of the water is evaporated, leaving all of the salt. When 7 Gallons of water and 14 gallons of salt are added, the resulting mixture is 33 1/3 % salt by volume. What is the value of x?