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#1 2013-01-21 21:39:12
- kjames
- Guest
mixture problem
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?
#2 2013-01-21 22:38:33
- phrontister
- Real Member
Offline
Re: mixture problem
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
#3 2013-01-21 22:47:42
- kjames
- Guest
Re: mixture problem
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!
#4 2013-01-21 23:47:33
- bobbym
- Administrator
Online
Re: mixture problem
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.
90% of mathematicians do not understand 90% of currently published mathematics.
I am willing to wager that over 75% of the new words that appeared were nothing more than spelling errors that caught on.
#5 2013-01-22 10:37:23
- phrontister
- Real Member
Offline
Re: mixture problem
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
#6 2013-01-22 10:49:22
- bobbym
- Administrator
Online
Re: mixture problem
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.
90% of mathematicians do not understand 90% of currently published mathematics.
I am willing to wager that over 75% of the new words that appeared were nothing more than spelling errors that caught on.