Source: Official Guide Revised GRE 1st Ed. Part 6; Set 2; #9


By weight, liquid A makes up 8 percent

By weight, liquid A makes up 8 percent of solution R and 18 percent of solution S. If 3 grams of solution R are mixed with 7 grams of solution S, then liquid A accounts for what percent of the weight of the resulting solution? 10%, 13%, 15%, 19%, 26%

3 Explanations


Ramlah Merchant

I didn't quite understand why we did 8% of 3g and 18% of 7g/3+7 here. Could you please explain how you got this formula?

Apr 26, 2017 • Comment

Cydney Seigerman, Magoosh Tutor

Hi Ramlah,

Happy to help :)

The formula is for weighted averages, which we can use to find out the percent of liquid A in the solution. In this question, we're told that Liquid A is 8% R and 18% S (by weight). Then, we're asked to consider a mixture of R and S: 3g R + 7g S.

As I mentioned above, we need to find out how much Liquid A is in this mixture of 3g R and 7g S. First, let's find the amount of liquid A in each of the two solutions:

Solution R: 0.08*3g = 0.24g
Solution S: 0.18*7g = 1.26g

So the total weight of A in the mixture is
0.24 + 1.26 = 1.5g

And the total weight of the entire mixture is
3g R + 7g S = 10g

Therefore the % weight of A in the mixture is

1.5g/10g * 100% = 15%

The formula combines the two steps above into one formula, leading to the same result :)

Hope this helps!

Apr 28, 2017 • Reply


Bilal Farooq

What topic would this be categorized as?

Sep 10, 2016 • Comment

Cydney Seigerman, Magoosh Tutor

Hi Bilal! This is a percent/fractions/ratio question from the Quant Section :)

Sep 11, 2016 • Reply


Gravatar Chris Lele, Magoosh Tutor

Oct 7, 2012 • Comment

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