Hi All,

While an Algebra approach (using the "weighted average" formula) would work nicely on this prompt, you can also answer it rather quickly by TESTing THE ANSWERS and using a bit of logic.

Here, we're going to mix 400 ounces of a 6% acid solution with X ounces of a 12% acid solution to form a 10% acid solution. We're asked for the value of X. The answers are all nice, round numbers, so we can take advantage of them....

Let's start with Answer B....

IF.....

X = 400 ounces

Then we'd have the same amount of each solution: 400 ounces of 6% and 400 ounces of 12% --> this would produce a (6%+12%)/2 = 9% mixture, which is TOO SMALL. X must be BIGGER. Eliminate Answers A and B.

Now, let's TEST Answer D...

IF....

X = 600 ounces

Then with 400 ounces of 6% and 600 ounces of 12%, we'd have...

[(400)(.06) + (600)(.12)]/(400 + 600) =

(24 + 72)/1000 = 96/1000 = 9.6%, which is TOO SMALL. X must be BIGGER. Eliminate C and D.

Final Answer:

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

Rich

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