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# Concrete mixture A is composed of 35 percent cement, 40 pecent sand an

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Senior Manager
Joined: 08 Jun 2013
Posts: 469
Location: India
GMAT 1: 200 Q1 V1
GPA: 3.82
WE: Engineering (Other)
Concrete mixture A is composed of 35 percent cement, 40 pecent sand an  [#permalink]

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Updated on: 17 Jul 2018, 10:46
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Difficulty:

25% (medium)

Question Stats:

80% (01:29) correct 20% (01:31) wrong based on 81 sessions

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Concrete mixture A is composed of 35 percent cement, 40 pecent sand and 25 percent gravel; concrete mixture B is composed of 15 percent cement, 30 percent sand and 55 percent gravel. If a mixture of A and B contains 25 percent cement, what percent of the weight of the mixture is A?

A 20%
B 33 1/3%
C 45%
D 50%
E 55 1/3%

_________________

It seems Kudos button not working correctly with all my posts...

Please check if it is working with this post......

is it?....

Anyways...Thanks for trying

Originally posted by Harshgmat on 16 Jul 2018, 07:45.
Last edited by Harshgmat on 17 Jul 2018, 10:46, edited 1 time in total.
VP
Joined: 07 Dec 2014
Posts: 1111
Re: Concrete mixture A is composed of 35 percent cement, 40 pecent sand an  [#permalink]

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16 Jul 2018, 18:33
Harshgmat wrote:
Concrete mixture A is composed of 35 percent cement, 40 pecent sand and 25 percent gravel; concrete mixture B is composed of 15 percent cement, 30 percent sand and 55 percent gravel. If a mixture of A and B contains 25 percent cement, what percent of the weight of the mixture is A?

A 20%
B 33 1/3%
C 45%
D 50%
E 55 1/3%

.35A+.15B=.25(A+B)
.10A=.10B
A=B
50%
D
Intern
Joined: 30 May 2018
Posts: 2
Re: Concrete mixture A is composed of 35 percent cement, 40 pecent sand an  [#permalink]

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16 Jul 2018, 22:16
I'm a bit confused - the response to this question is D and the spoiler says C... can someone help me figure out which one is correct? I got D but don't know if that is right.
Senior Manager
Joined: 08 Jun 2013
Posts: 469
Location: India
GMAT 1: 200 Q1 V1
GPA: 3.82
WE: Engineering (Other)
Re: Concrete mixture A is composed of 35 percent cement, 40 pecent sand an  [#permalink]

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17 Jul 2018, 10:48
sdilley wrote:
I'm a bit confused - the response to this question is D and the spoiler says C... can someone help me figure out which one is correct? I got D but don't know if that is right.

Thanks sdiley for pointing out the error.

It is being rectified now.
_________________

It seems Kudos button not working correctly with all my posts...

Please check if it is working with this post......

is it?....

Anyways...Thanks for trying

Senior SC Moderator
Joined: 22 May 2016
Posts: 2095
Concrete mixture A is composed of 35 percent cement, 40 pecent sand an  [#permalink]

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17 Jul 2018, 11:44
1
Harshgmat wrote:
Concrete mixture A is composed of 35 percent cement, 40 pecent sand and 25 percent gravel; concrete mixture B is composed of 15 percent cement, 30 percent sand and 55 percent gravel. If a mixture of A and B contains 25 percent cement, what percent of the weight of the mixture is A?

A 20%
B 33 1/3%
C 45%
D 50%
E 55 1/3%

We need to track only on cement percents, and we need either the ratio of A to B (part-part) or the ratio of A to (A + B) (part-whole) to answer the question.

Let % = percent cement in a mixture
A = volume / weight of A
B = volume / weight of B

(% A)(Vol A) + (% B)(Vol B) = (% A+B)(Vol A+B)

$$(.35*A)+(.15*B)=.25(A+B)$$
$$35A+15B=25A+25B$$
$$10A=10B$$

$$A=B$$ in the final mixture

$$A$$ is what percent of final mixture's weight?

Part-whole.
Percent A is $$\frac{A}{A+B}*100$$
From above $$A=B$$
Percent A:
$$\frac{A}{A+A}=\frac{1A}{2A}=\frac{1}{2}=(.50*100) = 50$$ percent

Part-Part
From above, $$A=B$$
Part + Part = Whole
Half + Half = Whole
A is half = 50%

That is, logically, a mixture containing only A and B and equal parts A and B is 50% A.

VP
Joined: 09 Mar 2016
Posts: 1069
Re: Concrete mixture A is composed of 35 percent cement, 40 pecent sand an  [#permalink]

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17 Jul 2018, 12:18
Harshgmat wrote:
Concrete mixture A is composed of 35 percent cement, 40 pecent sand and 25 percent gravel; concrete mixture B is composed of 15 percent cement, 30 percent sand and 55 percent gravel. If a mixture of A and B contains 25 percent cement, what percent of the weight of the mixture is A?

A 20%
B 33 1/3%
C 45%
D 50%
E 55 1/3%

i have used an alligator method

...35....………….15...

…………...25...………...

25-15..........35-15

…….. 10.......10...….

………...$$\frac{10}{10}$$

so D

is my solution correct
Math Expert
Joined: 02 Aug 2009
Posts: 7034
Re: Concrete mixture A is composed of 35 percent cement, 40 pecent sand an  [#permalink]

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17 Jul 2018, 18:10
1
Harshgmat wrote:
Concrete mixture A is composed of 35 percent cement, 40 pecent sand and 25 percent gravel; concrete mixture B is composed of 15 percent cement, 30 percent sand and 55 percent gravel. If a mixture of A and B contains 25 percent cement, what percent of the weight of the mixture is A?

A 20%
B 33 1/3%
C 45%
D 50%
E 55 1/3%

One of the best way to do this is by weighted average method
1) Here since presence of cement in final solution is being talked of, we require to concentrate only on cement.
2) the question becomes much easier when we see the % in three solutions..
A- 35
B- 15
Mix of A and B - 25
25 is half way between 15 and 35, so 50% of each

D
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3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html

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Re: Concrete mixture A is composed of 35 percent cement, 40 pecent sand an &nbs [#permalink] 17 Jul 2018, 18:10
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