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27 Jan 2022, 09:15
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C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
65%
(hard)
Question Stats:
65% (02:29) correct
35%
(02:37)
wrong
based on 236
sessions
History
Date
Time
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Not Attempted Yet
An alloy contains 24% of tin by weight. How much more tin to the nearest kg must be added to 100 kg of the alloy so that the percentage of tin may be doubled?
(A) 42
(B) 44
(C) 46
(D) 48
(E) 50
Are You Up For the Challenge: 700 Level Questions
(A) 42
(B) 44
(C) 46
(D) 48
(E) 50
Are You Up For the Challenge: 700 Level Questions
27 Jan 2022, 20:54
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24% tin by weight = 24 kg in 100kg
Let X kg be added.
\(\frac{24+x}{100+x}=0.48\)
x = 46
Answer = C
Posted from my mobile device
Let X kg be added.
\(\frac{24+x}{100+x}=0.48\)
x = 46
Answer = C
Posted from my mobile device
28 Jan 2022, 00:03
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Its a good question from the area of Percentage Application but however this is not a 700 level question for someone who has prepared through the area of Percentage and Percentage Applications. We would disagree with the perceived level of difficulty here. 
Lets have a look!
This alloy contains tin and some other metals.
24% of tin is present in the alloy by weight and this means 100-48 = 76% of other metals is present in the alloy.
So 24 kg of tin and 76kg of other metal is present in 100kg of alloy
The question says that we have to add more tin so that the percentage of tin should be doubled.
Instead of 24% of tin, we now want 48% of the tin and this implies the weight of the other metals though would remain same but would now constitute 100-48=52% of the alloy weight.
So 76kg would be 52% of the alloy weight.
GMAT Tip-On GMAT in such questions of Percentage Variation of different components(even in Mixture problems), always hold the quantity which doesn't change, is constant and takes you to the correct answer!
Here 52% of "other metals"= 76kg and hence 48%of tin = 76/52 * 48 = 70kg(Approx.)
So instead of 24 kg that tin occupied originally in the alloy, it now occupies 70 kg which implies an increase of 70-24 = 46kg by weight in the alloy.
As a Percentage this is = \(\frac{Weight of tin in the alloy }{ Total weight of the alloy}\)
= 46/100 * 100 =46%
(option c)
GMAT Advice-Do not worry on calculations. Most official questions would give you values that are easy on calculation. The takeaway from this question can be the method and the "thought behind".
(PS-The alternate equation based approach is already shown here by neerajgupta)
Hope you guys enjoyed the process and takeaways from the approach here
Devmitra Sen
GMAT Quant SME
Lets have a look!
This alloy contains tin and some other metals.
24% of tin is present in the alloy by weight and this means 100-48 = 76% of other metals is present in the alloy.
So 24 kg of tin and 76kg of other metal is present in 100kg of alloy
The question says that we have to add more tin so that the percentage of tin should be doubled.
Instead of 24% of tin, we now want 48% of the tin and this implies the weight of the other metals though would remain same but would now constitute 100-48=52% of the alloy weight.
So 76kg would be 52% of the alloy weight.
GMAT Tip-On GMAT in such questions of Percentage Variation of different components(even in Mixture problems), always hold the quantity which doesn't change, is constant and takes you to the correct answer!Here 52% of "other metals"= 76kg and hence 48%of tin = 76/52 * 48 = 70kg(Approx.)
So instead of 24 kg that tin occupied originally in the alloy, it now occupies 70 kg which implies an increase of 70-24 = 46kg by weight in the alloy.
As a Percentage this is = \(\frac{Weight of tin in the alloy }{ Total weight of the alloy}\)
= 46/100 * 100 =46%
(option c)
GMAT Advice-Do not worry on calculations. Most official questions would give you values that are easy on calculation. The takeaway from this question can be the method and the "thought behind".(PS-The alternate equation based approach is already shown here by neerajgupta)
Hope you guys enjoyed the process and takeaways from the approach here
Devmitra Sen
GMAT Quant SME
