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

Question

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%

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

gracie · Answer

.35A+.15B=.25(A+B)
.10A=.10B
A=B
50%
D

sdilley · Answer

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.

Helium · Answer

Thanks sdiley for pointing out the error.

It is being rectified now.

generis · Answer

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

Answer D

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.

Answer D

dave13 · Answer

i have used an alligator method

...35....………….15... …………...25...………... 25-15..........35-15 …….. 10.......10...…. ………... \frac{10}{10} so D

is my solution correct

chetan2u · Answer

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

AdarshSambare · Answer

Let's solve it by Allegations.
Focus on what is given for the mixture: percent of cement: 25
So we need to apply allegations for cement.

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

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

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

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