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At least how many grams of pure bronze must be...

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At least how many grams of pure bronze must be...

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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.

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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

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

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Post
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.

Answer: B

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Founder and CEO
scott@targettestprep.com



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