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# Two alloys A and B are composed of two basic elements. The

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30 Jun 2012, 20:15
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Two alloys A and B are composed of two basic elements. The ratios of the compositions of the two basic elements in the two alloys are 5 : 3 and 1 : 2, respectively. A new alloy X is formed by mixing the two alloys A and B in the ratio 4 : 3. What is the ratio of the composition of the two basic elements in alloy X ?

(A) 1 : 1
(B) 2 : 3
(C) 5 : 2
(D) 4 : 3
(E) 7 : 9
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01 Jul 2012, 00:33
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farukqmul wrote:
Two alloys A and B are composed of two basic elements. The ratios of the compositions of the two
basic elements in the two alloys are 5 : 3 and 1 : 2, respectively. A new alloy X is formed by mixing
the two alloys A and B in the ratio 4 : 3. What is the ratio of the composition of the two basic elements
in alloy X ?

(A) 1 : 1
(B) 2 : 3
(C) 5 : 2
(D) 4 : 3
(E) 7 : 9

Hi,

Proportion of 1st element in A = 5/8
Proportion of 1st element in B = 1/3
let, the proportion of 1st element in mixture = x
using allegations:
Attachment:

all.jpg [ 7.83 KiB | Viewed 15190 times ]

$$\frac {x-1/3}{5/8-x}= \frac 43$$
on solving, x=0.5
thus, proportion of two elements in the mixture is 1:1

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Re: Two alloys A and B are composed of two basic elements. The [#permalink]

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15 Aug 2012, 04:36
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farukqmul wrote:
Two alloys A and B are composed of two basic elements. The ratios of the compositions of the two basic elements in the two alloys are 5 : 3 and 1 : 2, respectively. A new alloy X is formed by mixing the two alloys A and B in the ratio 4 : 3. What is the ratio of the composition of the two basic elements in alloy X ?

(A) 1 : 1
(B) 2 : 3
(C) 5 : 2
(D) 4 : 3
(E) 7 : 9

Responding to a pm:

When you need to find the average, it is better to use the formula in its original form: Avg = (C1*w1 + C2*w2)/(w1 + w2)
Avg = [(5/8)*4 + (1/3)*3]/(4+3) = 1/2
Ratio of the 2 elements in the mixture = 1:1

Obviously the formula will work in the other form too though it is best to use that when you need to find the ratio of the weights. Using the formula in the other form: w1/w2 = (A2 - Aavg)/(Aavg - A1)
element 1 in A = 5/8
element 1 in B = 1/3
element 1 in mixture = x

4/3 = (1/3 - x) / (x - 5/8)
4/3(x - 5/8) = 1/3 - x
(7/3)x = 7/6
x = 1/2

Ratio of elements in the mixture = 1:1
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Get started with Veritas Prep GMAT On Demand for $199 Veritas Prep Reviews Director Joined: 22 Mar 2011 Posts: 612 WE: Science (Education) Followers: 98 Kudos [?]: 865 [5] , given: 43 Re: Two alloys A and B are composed of two basic elements. The [#permalink] ### Show Tags 15 Aug 2012, 05:00 5 This post received KUDOS 2 This post was BOOKMARKED farukqmul wrote: Two alloys A and B are composed of two basic elements. The ratios of the compositions of the two basic elements in the two alloys are 5 : 3 and 1 : 2, respectively. A new alloy X is formed by mixing the two alloys A and B in the ratio 4 : 3. What is the ratio of the composition of the two basic elements in alloy X ? (A) 1 : 1 (B) 2 : 3 (C) 5 : 2 (D) 4 : 3 (E) 7 : 9 Mixture A has a total of 5 + 3 = 8 parts. If in the final mixture this represents 4 parts, then the total number of parts in mixture B should be (8/4)*3 = 6. So, we should take of mixture B a quantity with 2 and 4 parts, respectively. This will give us in the final mixture (5 + 2) : (3 + 4), which means 7:7, or 1:1. Answer A. _________________ PhD in Applied Mathematics Love GMAT Quant questions and running. Intern Joined: 19 Feb 2012 Posts: 25 Location: India Concentration: Technology, General Management Schools: WBS '15 GMAT 1: 700 Q48 V38 GPA: 3.36 WE: Analyst (Computer Software) Followers: 0 Kudos [?]: 6 [1] , given: 7 Re: Two alloys A and B are composed of two basic elements. The [#permalink] ### Show Tags 29 Oct 2012, 01:48 1 This post received KUDOS Alloy A: Since F:S = 5:3, and 5+3=8, F/total = 5/8. Alloy B: Since F:S = 1:2, and 1+2 = 3, F/total = 1/3. Mixture T: A:B = 4:3. If we mix 8 units of A with 6 units of B, we get: Amount of F in alloy A = (5/8)8 = 5 units Amount of F in alloy B = (1/3)6 = 2 units. (Total F)/(Mixture T) = (5+2)/(8+6) = 7/14 = 1/2. Since 1/2 of the mixture is composed of F, F:S = 1:1. Intern Joined: 31 Oct 2012 Posts: 24 Followers: 0 Kudos [?]: 5 [0], given: 4 Re: Two alloys A and B are composed of two basic elements. The [#permalink] ### Show Tags 15 Dec 2012, 21:30 1 This post was BOOKMARKED Ratio of Elements A - 5:3 / 5x:3x B - 1:2 / 1y:2y Ratio of Alloys A+B - 4:3 ie. A:B = 4:3 (5x+3x):(1y+2y) = 4:3 8x:3y = 4:3 x:y = 1:2 => y = 2x Ratio of elements in (A+B) 1st element in A and B / 2nd Element in A and B (5x + y)/(3x + 2y) but y = 2x ie. 7x/7x = 1:1 Ans A Intern Joined: 24 Apr 2012 Posts: 48 Followers: 0 Kudos [?]: 22 [0], given: 1 Re: Two alloys A and B are composed of two basic elements. The [#permalink] ### Show Tags 16 Dec 2012, 03:01 let the two elements be 1 and 2,element 1 in alloy A =5/8 , element 1 in alloy B=1/3, element 1 in mixture=x, therefore 4/3=(1/3-x)/(5/8-x)= ½ so the answer is (A). _________________ www.mnemoniceducation.com TURN ON YOUR MINDS!!! VP Status: Been a long time guys... Joined: 03 Feb 2011 Posts: 1420 Location: United States (NY) Concentration: Finance, Marketing GPA: 3.75 Followers: 174 Kudos [?]: 1299 [0], given: 62 Re: Two alloys A and B are composed of two basic elements. The [#permalink] ### Show Tags 16 Dec 2012, 03:07 1 This post was BOOKMARKED Another approach to this problem is by weighted average. In such problems , it becomes easier if we stick to one metal only. So the compostion of first metal in A is 5/8 and and in B is 1/3. So when we combine A and B, the compostion will be between 5/8 and 1/3. Now in the diagram attached: The "distance" between the compositions of first metal in A and B is 7/24. The composition of the final mixture is given as 4:3 i.e. A's 4 parts and B's 3 parts. But when we interpret in the distance format, the sequence flips i.e. the distance between final mixture and A will be 3 units and that of between final mixture and B will be 4 units. Now to calculate the compostion of the first metal in X, add the 4 units to 1/3. i.e. $$4/7 *$$$$7/24$$ $$+1/3$$ OR subtract 3 units from 5/8 i.e. $$5/8 -$$ $$4/7$$$$* 7/24$$. This will come out as 50%. Therefore the other metal will also constitute 50%. Hence the ratio is 1:1. +1A Attachments solution.png [ 13.08 KiB | Viewed 13621 times ] _________________ Intern Joined: 05 Sep 2011 Posts: 7 Followers: 0 Kudos [?]: 1 [0], given: 1 Re: Two alloys A and B are composed of two basic elements. The [#permalink] ### Show Tags 10 Apr 2013, 20:19 VeritasPrepKarishma wrote: farukqmul wrote: Two alloys A and B are composed of two basic elements. The ratios of the compositions of the two basic elements in the two alloys are 5 : 3 and 1 : 2, respectively. A new alloy X is formed by mixing the two alloys A and B in the ratio 4 : 3. What is the ratio of the composition of the two basic elements in alloy X ? (A) 1 : 1 (B) 2 : 3 (C) 5 : 2 (D) 4 : 3 (E) 7 : 9 Responding to a pm: When you need to find the average, it is better to use the formula in its original form: Avg = (C1*w1 + C2*w2)/(w1 + w2) Avg = [(5/8)*4 + (1/3)*3]/(4+3) = 1/2 Ratio of the 2 elements in the mixture = 1:1 Obviously the formula will work in the other form too though it is best to use that when you need to find the ratio of the weights. Using the formula in the other form: w1/w2 = (A2 - Aavg)/(Aavg - A1) element 1 in A = 5/8 element 1 in B = 1/3 element 1 in mixture = x 4/3 = (1/3 - x) / (x - 5/8) 4/3(x - 5/8) = 1/3 - x (7/3)x = 7/6 x = 1/2 (You made a calculation error) Ratio of elements in the mixture = 1:1 Dear karishma thanks a lot. that's a great solution but one point is subtle to me. would you please explain which part of the question indicates that we should go with weighted average formula? thanks again in advance. Regards Posted from my mobile device Veritas Prep GMAT Instructor Joined: 16 Oct 2010 Posts: 7063 Location: Pune, India Followers: 2083 Kudos [?]: 13264 [0], given: 221 Re: Two alloys A and B are composed of two basic elements. The [#permalink] ### Show Tags 11 Apr 2013, 06:15 marzan2011 wrote: Dear karishma thanks a lot. that's a great solution but one point is subtle to me. would you please explain which part of the question indicates that we should go with weighted average formula? thanks again in advance. Regards Posted from my mobile device It's a matter of practice. You will never be given 'find the weighted average'. When you have two things (classes, groups, mixtures, solutions) and they talk about the total, average or something, that should give you a hint that weighted average might work here. _________________ Karishma Veritas Prep | GMAT Instructor My Blog Get started with Veritas Prep GMAT On Demand for$199

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Re: Two alloys A and B are composed of two basic elements. The [#permalink]

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04 Aug 2015, 17:29
VeritasPrepKarishma wrote:
farukqmul wrote:
Two alloys A and B are composed of two basic elements. The ratios of the compositions of the two basic elements in the two alloys are 5 : 3 and 1 : 2, respectively. A new alloy X is formed by mixing the two alloys A and B in the ratio 4 : 3. What is the ratio of the composition of the two basic elements in alloy X ?

(A) 1 : 1
(B) 2 : 3
(C) 5 : 2
(D) 4 : 3
(E) 7 : 9

Responding to a pm:

When you need to find the average, it is better to use the formula in its original form: Avg = (C1*w1 + C2*w2)/(w1 + w2)
Avg = [(5/8)*4 + (1/3)*3]/(4+3) = 1/2
Ratio of the 2 elements in the mixture = 1:1

Obviously the formula will work in the other form too though it is best to use that when you need to find the ratio of the weights. Using the formula in the other form: w1/w2 = (A2 - Aavg)/(Aavg - A1)
element 1 in A = 5/8
element 1 in B = 1/3
element 1 in mixture = x

4/3 = (1/3 - x) / (x - 5/8)
4/3(x - 5/8) = 1/3 - x
(7/3)x = 7/6
x = 1/2

Ratio of elements in the mixture = 1:1

Hi,

Thanks alot for the great solution, just one quick question, if we are getting the x (which is the amount of A in mixture) = 1/2, then how are we getting to ratio as 1:1?
Is it because 1/2 stands for A/A+B so 1/1+1 and hence A and B are in ration 1:1

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Re: Two alloys A and B are composed of two basic elements. The [#permalink]

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04 Aug 2015, 20:39
neeraj609 wrote:
VeritasPrepKarishma wrote:
farukqmul wrote:
Two alloys A and B are composed of two basic elements. The ratios of the compositions of the two basic elements in the two alloys are 5 : 3 and 1 : 2, respectively. A new alloy X is formed by mixing the two alloys A and B in the ratio 4 : 3. What is the ratio of the composition of the two basic elements in alloy X ?

(A) 1 : 1
(B) 2 : 3
(C) 5 : 2
(D) 4 : 3
(E) 7 : 9

Responding to a pm:

When you need to find the average, it is better to use the formula in its original form: Avg = (C1*w1 + C2*w2)/(w1 + w2)
Avg = [(5/8)*4 + (1/3)*3]/(4+3) = 1/2
Ratio of the 2 elements in the mixture = 1:1

Obviously the formula will work in the other form too though it is best to use that when you need to find the ratio of the weights. Using the formula in the other form: w1/w2 = (A2 - Aavg)/(Aavg - A1)
element 1 in A = 5/8
element 1 in B = 1/3
element 1 in mixture = x

4/3 = (1/3 - x) / (x - 5/8)
4/3(x - 5/8) = 1/3 - x
(7/3)x = 7/6
x = 1/2

Ratio of elements in the mixture = 1:1

Hi,

Thanks alot for the great solution, just one quick question, if we are getting the x (which is the amount of A in mixture) = 1/2, then how are we getting to ratio as 1:1?
Is it because 1/2 stands for A/A+B so 1/1+1 and hence A and B are in ration 1:1

Yes, element 1 in mixture is element 1 in total.
So element 1 is 1 part out of 2 total parts. The other part must be the other basic element.
_________________

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Veritas Prep | GMAT Instructor
My Blog

Get started with Veritas Prep GMAT On Demand for $199 Veritas Prep Reviews Senior Manager Joined: 07 Dec 2014 Posts: 454 Followers: 3 Kudos [?]: 76 [0], given: 2 Re: Two alloys A and B are composed of two basic elements. The [#permalink] ### Show Tags 29 Sep 2015, 12:37 let E=element 1 4(5/8)+3(1/3)=7E E=1/2 ratio between elements=1:1 GMAT Club Legend Joined: 09 Sep 2013 Posts: 12867 Followers: 559 Kudos [?]: 157 [0], given: 0 Re: Two alloys A and B are composed of two basic elements. The [#permalink] ### Show Tags 09 Oct 2016, 09:54 Hello from the GMAT Club BumpBot! Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos). Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email. _________________ Veritas Prep GMAT Instructor Joined: 16 Oct 2010 Posts: 7063 Location: Pune, India Followers: 2083 Kudos [?]: 13264 [1] , given: 221 Two alloys A and B are composed of two basic elements. The [#permalink] ### Show Tags 12 Oct 2016, 03:10 1 This post received KUDOS Expert's post VeritasPrepKarishma wrote: farukqmul wrote: Two alloys A and B are composed of two basic elements. The ratios of the compositions of the two basic elements in the two alloys are 5 : 3 and 1 : 2, respectively. A new alloy X is formed by mixing the two alloys A and B in the ratio 4 : 3. What is the ratio of the composition of the two basic elements in alloy X ? (A) 1 : 1 (B) 2 : 3 (C) 5 : 2 (D) 4 : 3 (E) 7 : 9 Responding to a pm: When you need to find the average, it is better to use the formula in its original form: Avg = (C1*w1 + C2*w2)/(w1 + w2) Avg = [(5/8)*4 + (1/3)*3]/(4+3) = 1/2 Ratio of the 2 elements in the mixture = 1:1 Obviously the formula will work in the other form too though it is best to use that when you need to find the ratio of the weights. Using the formula in the other form: w1/w2 = (A2 - Aavg)/(Aavg - A1) element 1 in A = 5/8 element 1 in B = 1/3 element 1 in mixture = x 4/3 = (1/3 - x) / (x - 5/8) 4/3(x - 5/8) = 1/3 - x (7/3)x = 7/6 x = 1/2 (You made a calculation error) Ratio of elements in the mixture = 1:1 Responding to a pm: Quote: I don't completely understand your solution. Why did you do Avg = [(5/8)*4 + (1/3)*3]/(4+3) rather than Avg = [(5/8)*4 + (1/3)*4]/(4+3)? The 1/3 also refers to the first part of the ratio doesn't it? The formula is $$Cavg = \frac{(C1*w1 + C2*w2)}{(w1 + w2)}$$ The ratios of the compositions of the two basic elements in the two alloys are 5 : 3 (first element is 5/8 of Total) and 1 : 2 (first element is 1/3 of Total) "A new alloy X is formed by mixing the two alloys A and B in the ratio 4 : 3" - This implies that w1:w2 = 4:3 $$Cavg = \frac{(5/8)*4 + (1/3)*3}{4 + 3}$$ _________________ Karishma Veritas Prep | GMAT Instructor My Blog Get started with Veritas Prep GMAT On Demand for$199

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Two alloys A and B are composed of two basic elements. The   [#permalink] 12 Oct 2016, 03:10
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