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An alloy contains tin and copper in the ratio of 4:5 . If tin has 20%

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An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink]

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An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% impurity and copper has 58% , what is the avg impurity percentage ?

A. 20%

B. 41.1%

C. 35%

D. 38%

E. 43.1%
[Reveal] Spoiler: OA

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Kudos [?]: 132894 [0], given: 12391

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An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink]

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Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink]

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New post 04 Mar 2014, 01:51
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Impurity in tin = 20% of 4/9 = 80/900
Impurity in Cu = 58% of 5/9 = 290/900

Total Impurity = 380/900. Percent = 380/9 = 41.2
Answer = B
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Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink]

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New post 29 Mar 2015, 07:52
Bunuel wrote:
aimlockfire1 wrote:
An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% impurity and copper has 58% , what is the avg impurity percentage ?

a) 20%

b) 41.1%

c) 35%

d) 38%

e) 43.1%


(4*0.2 + 5*0.58)/(4+5) = ~41%.

Answer: B.


Tin and copper are in ratio of 4:5. So let total mixture be 4+5 = 9.
So, tin = 4 and copper = 5.
Now, tin has 20% impurity = 20% * 4 = 0.8
Also, copper has 58% impurity = 58% * 5 = 2.9
Average = (0.8 + 2.9)/(4+5)
= 3.7/9
= 0.411
= 41.1%

Hence option (B).

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Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink]

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New post 18 May 2015, 10:18
An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% impurity and copper has 58% , what is the avg impurity percentage ?

a) 20%

b) 41.1%

c) 35%

d) 38%

e) 43.1%



The problem is on ratio / Proportion but look closely it can be solved with weighted average concept

(4*0.2 + 5*0.58)/(4+5) = ~41%.

Answer: B.

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Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink]

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New post 18 May 2015, 10:46
Its a 10sec Question.
Because tin:Copper is in the ratio 4:5, there is more of Copper and hence more impurities from Copper in the final alloy. Since Copper has 58% impurities, the overall average should be closer to 58%, which narrows down the options to B or E. Since T:C is close to 1 (4:5), we want to pick the option closer to the middle but more towards C, which is 42%. Hence option B

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Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink]

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New post 26 May 2016, 19:19
Bunuel wrote:
aimlockfire1 wrote:
An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% impurity and copper has 58% , what is the avg impurity percentage ?

a) 20%

b) 41.1%

c) 35%

d) 38%

e) 43.1%


(4*0.2 + 5*0.58)/(4+5) = ~41%.

Answer: B.

Can be done with weighted avg. formula
w1/w2=(a2-avg)/(avg-a1)
4/5=(58-x)/(x-20)
x=41.1
Ans B

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Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink]

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Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20%   [#permalink] 14 Oct 2017, 01:50
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