Hi All,

We're told that Solution A is 40% chlorine by volume, and Solution B is 60% chlorine by volume and that a tank currently holds 40 gallons of Solution A. We're asked for the number of gallons of Solution B must be added so that the liquid in the tank becomes 50% chlorine. This is a 'Weighted Average' question and can be solved in a number of different ways. Based on the percentages involved, just a bit of logic and Arithmetic is all that's needed to get the correct answer.

When averaging two percentages - as we are in this question - if we have an EQUAL amount of each item, then the average will be the average of the two percentages. For example, if we have the SAME amount of a 10% solution and a 20% solution, then mixing the two solutions together will gives us a total that is (10+20)/2 = a 15% solution.

In this prompt, we're mixing a 40% solution and a 60% solution. Since the result will be a 50% solution - which is the EXACT average of 40 and 60, we know that we have the SAME amount of Solution A and Solution B. The prompt tells us that we have 40 gallons of A, so we will need 40 gallons of B to hit that 50% average.

Final Answer: A

GMAT assassins aren't born, they're made,
Rich