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100 points for $49 worth of Veritas practice GMATs FREE VERITAS PRACTICE GMAT EXAMS Earn 10 Points Per Post Earn 10 Points Per Thanks Earn 10 Points Per Upvote ## At least how many grams of pure bronze must be... tagged by: swerve ##### This topic has 2 expert replies and 0 member replies ### Top Member ## At least how many grams of pure bronze must be... At least how many grams of pure bronze must be alloyed with 387 grams of pure copper to create an alloy that is no more than 90% copper? A. 13 B. 43 C. 103 D. 348 E. 430 The OA is B. Please, can any expert explain this PS question for me? I tried the following, Can I say that 387 + x grams = y grams, and 387 = 0.9y then y = 430. Finally, 387 + x = 430 x = 430 - 387 = 43. I need your help. Thanks. ### GMAT/MBA Expert Legendary Member Joined 14 Jan 2015 Posted: 2667 messages Followed by: 122 members Upvotes: 1153 GMAT Score: 770 swerve wrote: At least how many grams of pure bronze must be alloyed with 387 grams of pure copper to create an alloy that is no more than 90% copper? A. 13 B. 43 C. 103 D. 348 E. 430 The OA is B. Please, can any expert explain this PS question for me? I tried the following, Can I say that 387 + x grams = y grams, and 387 = 0.9y then y = 430. Finally, 387 + x = 430 x = 430 - 387 = 43. I need your help. Thanks. A bit of logic eliminates most of the answer choices. Clearly, D and E would yield a mixture with much less than 90% copper. And if we estimate, we can see the same is true of C - if a mixture were 400 grams copper and you added 100 grams of bronze, the total mixture of 500 grams would be only 80% copper. C is out. Now you only have to test one of the two remaining options. Say you tried A. If you added 13 grams of bronze, the total mixture would be 387 + 13 = 400 grams. If it were 90% copper, it would have had .9 * 400 = 360 grams copper. If there's actually 387 grams, there's clearly more than 90% copper. A is out. You're left with B _________________ Veritas Prep | GMAT Instructor Veritas Prep Reviews Save$100 off any live Veritas Prep GMAT Course

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### GMAT/MBA Expert

GMAT Instructor
Joined
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Posted:
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Followed by:
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swerve wrote:
At least how many grams of pure bronze must be alloyed with 387 grams of pure copper to create an alloy that is no more than 90% copper?

A. 13
B. 43
C. 103
D. 348
E. 430

We can let n = the number of grams of pure bronze needed and create the equation:

387/(387 + n) = 9/10

3870 = 9(387 + n)

430 = 387 + n

43 = n

Alternate Solution:

We can let x = the total minimum weight of the alloy and create the equation:

0.9x = 387

9x = 3870

x = 3870/9

x = 430

Since the total minimum weight of the alloy must be 430 grams, we see that the minimum amount of bronze must be 430 - 387 = 43 grams.

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Scott Woodbury-Stewart
Founder and CEO
scott@targettestprep.com

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