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Retired Moderator Joined: 07 Jun 2014
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GRE 1: Q167 V156 WE: Business Development (Energy and Utilities)
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A makes up 8 percent of solution R and 18 percent [#permalink]
Expert's post 00:00

Question Stats: 83% (01:27) correct 16% (01:30) wrong based on 115 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
[Reveal] Spoiler: OA

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Sandy
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Try our free Online GRE Test Retired Moderator Joined: 07 Jun 2014
Posts: 4803
GRE 1: Q167 V156 WE: Business Development (Energy and Utilities)
Followers: 175

Kudos [?]: 3036  , given: 394

Re: A makes up 8 percent of solution R and 18 percent [#permalink]
1
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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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Sandy
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Intern Joined: 14 Jul 2016
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Re: A makes up 8 percent of solution R and 18 percent [#permalink]
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.
Intern Joined: 01 Aug 2016
Posts: 2
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Re: A makes up 8 percent of solution R and 18 percent [#permalink]
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.
Retired Moderator Joined: 07 Jun 2014
Posts: 4803
GRE 1: Q167 V156 WE: Business Development (Energy and Utilities)
Followers: 175

Kudos [?]: 3036 , given: 394

Re: A makes up 8 percent of solution R and 18 percent [#permalink]
Expert's post
Fixed. Thanks for pointing that out.

Hope you find this forum informative and useful.

Regards,
_________________

Sandy
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Intern Joined: 01 Aug 2016
Posts: 2
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Re: A makes up 8 percent of solution R and 18 percent [#permalink]
sandy wrote:
Fixed. Thanks for pointing that out.

Hope you find this forum informative and useful.

Regards,

Thanks .......Junayed GRE Instructor Joined: 10 Apr 2015
Posts: 3907
Followers: 164

Kudos [?]: 4771  , given: 70

Re: A makes up 8 percent of solution R and 18 percent [#permalink]
1
KUDOS
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%

Cheers,
Brent

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Brent Hanneson – Creator of greenlighttestprep.com  GRE Instructor Joined: 10 Apr 2015
Posts: 3907
Followers: 164

Kudos [?]: 4771  , given: 70

Re: A makes up 8 percent of solution R and 18 percent [#permalink]
1
KUDOS
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%

Cheers,
Brent

RELATED VIDEO FROM MY COURSE

_________________

Brent Hanneson – Creator of greenlighttestprep.com Manager  Joined: 19 Nov 2018
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Re: A makes up 8 percent of solution R and 18 percent [#permalink]
Sandy, regarding: 3∗8/(3+7)

Shouldn't it be (3*0.8 + 0.18*7)/3+7

which would give (0.24 + 1.26)/10

= 1.5/10

= 0.15

= 15%
Senior Manager  Joined: 10 Feb 2020
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Re: A makes up 8 percent of solution R and 18 percent [#permalink]
=(portion) * (percent) of A + (portion) * (percent) of B
= 3/(3+7) * .08 + 7/(3+7) * 0.18
= .024 + .126
= .15 = 15%

Other Method:

R(3)-----------------S(7)
8%----------x--------18%
x-8------------------18-x

18-x/x-8 = 3/7
x=15
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