Brass is an alloy of copper and zinc whose proportions can vary to ach

Question

Brass is an alloy of copper and zinc whose proportions can vary to achieve different properties. Mix A, which weighs 50 kg, consists of 66% copper and 34% zinc in one such blend. This mix must be adjusted to increase its hardness by adding the maximum possible amount of zinc while ensuring that the zinc content does not exceed the weight of the copper in the new mix. Another blend, Mix B, contains 40% copper and 60% zinc and can be combined with Mix A to achieve the desired proportion. 
 
Select the weight of pure zinc in kg that would be added by combining Mix A with either zinc alone or with Mix B to meet the above requirement. Make only two selections, one from each column.

Armaan209 · Accepted Answer

Here if the solution

Bismuth83 · Answer

1. We are asked to  find the maximum weight of zinc that was added  (without breaking the requirement) after doing a method - either adding only zinc or adding Mix B.  
 
 2. It is known that amount of copper in Mix A is 66% of 50kg or 33kg and the amount of zinc in Mix A is 50-33 = 17kg. Our requirement states that the total amount of copper is greater than or equal to the total amount of zinc.  
 
 3. Let’s consider both methods:

Method 1: Pure Zinc. Since no copper is added, the amount of copper will be 33 kg. Let the amount of pure zinc added be Z. Then the total amount of zinc (the maximum that there can be) will be equal to 17+Z = 33 -> Z = 16 kg. So, our answer will be   16  .

Method 2: Mix B. Mix B contains 40% copper and 60% zinc. To balance the mix, if B kg of Mix B is added, then 0.6B will be added to the existing 17 kg of zinc. Then the total amount of zinc (the maximum that there can be) will be equal to 17 + 0.6B = 33+0.4B -> 0.2B = 16 -> B = 80. This means that the amount of zinc added 0.6B = 0.6*80 = 48. So, our answer will be   48  .

NoeticImbecile · Answer

Hello  Armaan209 . I also used alligation for this problem. Can you please explain why did you take total weight of zinc as 50kgs in RO1 when its given that zinc is 34% of 50kgs, which works out as 17kgs

bibhuti750 · Answer

hi

can you please explain this.

cheshire · Answer

You take the complete weight of alloy A because you are adding pure zinc to it. Your goal is to create a harder alloy so you take the original alloy in its entirety, not just the zinc composition.

cheshire · Answer

Mixing 50 kg of Mix A (34% Zn) with pure Zn (100% Zn) to get 50% Zn. 
 
 Cl=34%, Ch=100%, target Cm=50%. 
 Parts of high (pure Zn) = Cm−Cl=50−34=16 
 Parts of low (Mix A) = Ch−Cm=100−50=50 
 Ratio Zn : Mix A = 16:50=8:25 
 Since Mix A is fixed at 50 kg (that’s “25 parts”), one “part” = 50/25=2 kg → pure Zn = 8×2=16

Mixing 50 kg of Mix A (34% Zn) with Mix B (60% Zn) to get 50% Zn. 
 Here “lower” is Mix A at 34%, “higher” is Mix B at 60%, target 50%. 
 Parts of Mix B (high) = 50−34=16 
 Parts of Mix A (low) = 60−50=10 
 Ratio B : A = 16:10=8:5 
 Mix A is 50 kg (“5 parts”), so one part = 50/5=10 kg → Mix B = 8×10=80 kg, which contributes 0.6×80=48 kg of Zn.

I assume you know how Alligation works (the process used above)? If you don't I would look up a more comprehensive explanation of the method rather than just this application as its useful in a lot of situations.

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Brass is an alloy of copper and zinc whose proportions can vary to ach

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Zinc	Mix B
		8
		16
		32
		48
		50
		72

GMAT Two-part Analysis (TPA) Questions

Brass is an alloy of copper and zinc whose proportions can vary to ach

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