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.
At least how many grams of pure bronze must be...
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- DavidG@VeritasPrep
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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.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.
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
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- Scott@TargetTestPrep
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We can let n = the number of grams of pure bronze needed and create the equation: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
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.
Answer: B
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