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

tagged by: swerve

### 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.

### GMAT/MBA Expert

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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.

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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