Question 190406: This problem is from a computer-based textbook. An alloy of tin and copper is 16 percent tin. How much tin( to the nearest tenth) must be added to make an alloy that is 18 percent tin?
I'm really having trouble doing problems with 2 unknowns. I think I need to know how much copper there is, but I'm not sure how to do that. Please help. Thank you.
Answer by ptaylor(2198)   (Show Source):
You can put this solution on YOUR website!
Let A=amount of alloy that we have to start with (I think you left this out)
and Let x=amount of tin that needs to be added
Now we know that the amount of copper before we add tin(0.84A) has to equal the amount of copper after we add tin ((0.82(A+x)). So, our equation to solve is:
0.84A=0.82(A+x) get rid of parens
0.84A=0.82A+0.82x subtract 0.82A from each side
0.84A-0.82A=0.82x
0.82x=0.02A divide each side by 0.82
x=0.024A
As you can see here, the amount of tin that needs to be added will depend upon the original amount of the alloy and you did not include that number.
Hope this helps---ptaylor
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