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A makes up 8 percent of solution R and 18 percent [#permalink]
14 Dec 2015, 06:12

Expert's post

00:00

Question Stats:

78% (01:22) correct
21% (00:52) wrong based on 28 sessions

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? A. 10% B. 13% C. 15% D. 19% E. 26%

Practice Questions Question: 9 Page: 152 Difficulty: medium

Re: A makes up 8 percent of solution R and 18 percent [#permalink]
14 Dec 2015, 06:19

Expert's post

Solution

Here we are mixing two solutions R and S. the percentages of A in the two solutions are 8% and 18% respectively. So the resultant mixture will also contain liquid A. and it will also depend on the weights of R and S

We can write that %A in mixture = \(\frac{(3 * 8% + 7 *18%)}{(3 +7)}\) the result is almost equal to 15%. Hence 15% is the right answer.
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Re: A makes up 8 percent of solution R and 18 percent [#permalink]
14 Jul 2016, 08:22

I chose Answer C, but it was considered wrong!

sandy wrote:

Solution

Here we are mixing two solutions R and S. the percentages of A in the two solutions are 8% and 18% respectively. So the resultant mixture will also contain liquid A. and it will also depend on the weights of R and S

We can write that %A in mixture = \(\frac{(3 * 8% + 7 *18%)}{(3 +7)}\) the result is almost equal to 15%. Hence 15% is the right answer.

Re: A makes up 8 percent of solution R and 18 percent [#permalink]
01 Aug 2016, 10:51

sandy wrote:

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? A. 10% B. 13% C. 15% D. 19% E. 26%

Practice Questions Question: 9 Page: 152 Difficulty: medium

Why does it shows "E" as the correct answer,whereas,it should be "C". Answer is incorrect.

Re: A makes up 8 percent of solution R and 18 percent [#permalink]
11 Feb 2019, 11:14

Expert's post

sandy wrote:

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? A. 10% B. 13% C. 15% D. 19% E. 26%

When solving mixture questions, I often find it useful to sketch the solutions with the ingredients SEPARATED.

We have 3 grams of solution R, which is comprised of 8% liquid A So, 8% of the 3 grams will be liquid A 8% of 3 = (0.08)(3) = 0.24 So, solution R consists of 0.24 grams of liquid A

We'll now ADD 7 grams of solution S, which is comprised of 18% liquid A 18% of 7 = (0.18)(7) = 1.26 So, solution S consists of 1.26 grams of liquid A

Liquid A accounts for what percent of the weight of the resulting solution? When we combine the solutions BY PARTS, we get the following:

So, liquid A makes up 1.5 grams of the 10 grams in the resulting solution. 1.5/10 = 15/100 = 15%

Answer: C

Cheers, Brent

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Re: A makes up 8 percent of solution R and 18 percent [#permalink]
11 Feb 2019, 11:20

Expert's post

sandy wrote:

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? A. 10% B. 13% C. 15% D. 19% E. 26%

Another approach is to use the Weighted Averages formula:

Weighted average of groups combined = (group A proportion)(group A average) + (group B proportion)(group B average) + (group C proportion)(group C average) + ...

The weight of the resulting solution is 10 grams (3 grams + 7 grams = 10 grams)

Solution R makes up 3/10 of the resulting solution. Solution R is comprised of 8% liquid A

Solution S makes up 7/10 of the resulting solution. Solution S is comprised of 18% liquid A

Apply the formula to get: % liquid A in final solution = (3/10)(8) + (7/10)(18) = 24/10 + 126/10 = 150/10 = 15%

Answer: C

Cheers, Brent

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_________________

Brent Hanneson – Creator of greenlighttestprep.com Sign up for my free GRE Question of the Dayemails