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**kjames****Guest**

How much copper and how much magnesium should be added to 200 lbs of an alloy containing 20% copper and 40% magnesium to produce an alloy containing 24%copper and 50% magnesium?

**phrontister****Real Member**- From: The Land of Tomorrow
- Registered: 2009-07-12
- Posts: 3,853

Hi kjames,

Sorry, but I'm tied up doing something else for quite a while, and so I can only give a quick answer that isn't exact (it's a decimal approximation), and as I got it with Excel's Goal Seek I can't give the method you probably want, either.

Here's what I got:

Copper: add 33.846153846154 lbs

Magnesium: add 73.846153846154 lbs

"The good news about computers is that they do what you tell them to do. The bad news is that they do what you tell them to do." - Ted Nelson

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**kjames****Guest**

Thanks for giving time in answering my question but can somebody else show me the solution so that I can learn how to do it..thank you!

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 88,788

Hi;

Let c be the amount of copper to be added and m the amount of magnesium to be added

c = 440 / 13, m = 960 / 13

**In mathematics, you don't understand things. You just get used to them.**

**I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.**

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**phrontister****Real Member**- From: The Land of Tomorrow
- Registered: 2009-07-12
- Posts: 3,853

Hi,

Nice and compact, Bobby! I didn't think of going that way.

This is how I've done it:

Initially...

Copper = 20% of 200 lbs = 40 lbs

Magnesium = 40% of 200 lbs = 80 lbs

Other = 40% of 200 lbs = 80 lbs

Totals = 100% = 200 lbs

When added...

Copper = 24% of x lbs

Magnesium = 40% of x lbs

Other = 26% of x lbs, ∴ x = 80/26% lbs

Total = 100%

Copper added = 24% of x = (24*80/26)-40 lbs = (960/13)-40 = 440/13

Magnesium added = 50% of x = (50*80/26)-80 lbs = (2000/13)-80 = 960/13

"The good news about computers is that they do what you tell them to do. The bad news is that they do what you tell them to do." - Ted Nelson

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**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 88,788

Hi;

There are many ways to solve a problem. That should be enough to make the OP happy!

**In mathematics, you don't understand things. You just get used to them.**

**I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.**

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