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Two alloys, A and B were made by mixing Copper and Zinc 07 Aug 2022, 03:41
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65% (02:50) correct 35% (03:23) wrong based on 55 sessions

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Two alloys, A and B, were made by mixing Copper and Zinc. A total of 90 Kgs of Copper and 270 Kgs of Zinc were used for preparation of alloys A and B. The ratio of Copper to Zinc in alloy A was 1 : 5, while the ratio of Zinc to Copper in alloy B was 17 : 7. What quantity of Copper (in Kgs) was contained in the alloy A?

A. 20
B. 30
C. 50
D. 60
E. 80

(adapted from gmatfree)

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Two alloys, A and B were made by mixing Copper and Zinc 30 Aug 2022, 09:41
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Total Copper = 90
Total Zinc = 270
Total Copper + Total Zinc = 360
A contains Copper and Zinc in the ratio of 1/5 ; Total copper and zinc in A = x+5x=6x
B contains Copper and Zinc in the ratio of 7/17; Total copper and zinc in B = 7y+17y=24y

6x+24y=360
x+4y=60
x+7y=90
3y=30; y=10; x=20
copper in A=x=20
Option A
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Two alloys, A and B were made by mixing Copper and Zinc 31 Aug 2022, 14:14
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wadhwakaran
Total Copper = 90
Total Zinc = 270
Total Copper + Total Zinc = 360
A contains Copper and Zinc in the ratio of 1/5 ; Total copper and zinc in A = x+5x=6x
B contains Copper and Zinc in the ratio of 7/17; Total copper and zinc in B = 7y+17y=24y

6x+24y=360
x+4y=60
x+7y=90
3y=30; y=10; x=20
copper in A=x=20
Option A
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Can you let me know how you solved the last but 2 steps?
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Two alloys, A and B were made by mixing Copper and Zinc 03 Sep 2022, 10:52
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In combined … C:Z = 90:270 = 1:3
In Alloy A: C:Z = 1:5
In Alloy B: C:Z = 7:17
So, using weighted avg method ( scale method), considering the copper part,
A combined B
1/6 ---------- 1/4 -----------7/24
2 1
So, Copper in A : Copper in B = 1:2
So, 90 Kg copper distributed in A and B with ratio 1:2
So, in A, copper qty = 90 x 1/3 = 30.
So, Ans in B.
However, OA is A.
Bunuel and KarishmaB, am I doing any mistake?
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Two alloys, A and B were made by mixing Copper and Zinc 05 Sep 2022, 00:31
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bobnil
In combined … C:Z = 90:270 = 1:3
In Alloy A: C:Z = 1:5
In Alloy B: C:Z = 7:17
So, using weighted avg method ( scale method), considering the copper part,
A combined B
1/6 ---------- 1/4 -----------7/24
2 1
So, Copper in A : Copper in B = 1:2
So, 90 Kg copper distributed in A and B with ratio 1:2
So, in A, copper qty = 90 x 1/3 = 30.
So, Ans in B.
However, OA is A.
Bunuel and KarishmaB, am I doing any mistake?
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We must understand what the obtained ratio 1:2 is. It is the ratio of weight of alloy A : weight of alloy B
Recall the weighted average formula. In that, we mix two alloys and get the total mixture and w1/w2 is the ratio of weights in which the two alloys were mixed. Here we are using the same concept but we have the mixture and we are separating out the two alloys.

So of the total (90 + 270 kg = ) 360 kg of mixture, alloy A was 120 kg and alloy B was 240 kg and they were together 360 kg.

If alloy A was 120 kg with Copper : Zinc as 1:5, then amount of copper in alloy A was 20 kg.
We are
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Two alloys, A and B were made by mixing Copper and Zinc 10 Sep 2022, 05:07
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RogerMathew96
wadhwakaran
Total Copper = 90
Total Zinc = 270
Total Copper + Total Zinc = 360
A contains Copper and Zinc in the ratio of 1/5 ; Total copper and zinc in A = x+5x=6x
B contains Copper and Zinc in the ratio of 7/17; Total copper and zinc in B = 7y+17y=24y

6x+24y=360
x+4y=60
x+7y=90
3y=30; y=10; x=20
copper in A=x=20
Option A


Can you let me know how you solved the last but 2 steps?
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