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Posted by VDub on Sep-29-2008 21:14:

Math Question...

OK all you smart college types...

Billy has two chunks of copper alloy...

one is 60% copper and the other is 40% copper...

He melts the two together and the resulting piece weighs 400g and is 51% copper...

How much did each of the original chunks weigh????


Posted by junkie_vince on Sep-29-2008 21:17:

who the fuck is billy?


Posted by Vivid Boy on Sep-29-2008 21:17:

Re: Math Question...

quote:
Originally posted by VDub
OK all you smart college types...

Billy has two chunks of copper alloy...

one is 60% copper and the other is 40% copper...

He melts the two together and the resulting piece weighs 400g and is 51% copper...

How much did each of the original chunks weigh????


george brown college, plumbing?


Posted by VDub on Sep-29-2008 21:22:

Re: Re: Math Question...

quote:
Originally posted by Vivid Boy
george brown college, plumbing?


LOL...

Actually I work right kitty corner to George Brown...

And I'm not a plumber....

This was a question on my lil bro's homework and he needed help...

I think I figured it out but wanted to confirm...


Posted by VDub on Sep-29-2008 21:23:

quote:
Originally posted by junkie_vince
who the fuck is billy?


Billy's your boy...


Posted by cammaxwell on Sep-29-2008 21:26:

204g


Posted by VDub on Sep-29-2008 21:30:

quote:
Originally posted by cammaxwell
204g


There are two pieces........

So you're saying that the second one was 196g???


Posted by cammaxwell on Sep-29-2008 21:39:

sorry, I read the question wrong...

one peice is 220g (60%)

one peice is 180g (40%)


Posted by ChemEnhanced on Sep-29-2008 21:43:

my head is going to explode.


Posted by VDub on Sep-29-2008 21:44:

quote:
Originally posted by cammaxwell
sorry, I read the question wrong...

one peice is 220g (60%)

one peice is 180g (40%)


no...you're reading it wrong...

The 60 and 40% are the copper content of the original 2 pieces...

When they are melted, the resulting piece is 51% copper...


Posted by VDub on Sep-29-2008 21:45:

quote:
Originally posted by ChemEnhanced
my head is going to explode.


I'm glad ppl are feeling like I did last night with this problem....


Posted by cammaxwell on Sep-29-2008 21:48:

quote:
Originally posted by cammaxwell
sorry, I read the question wrong...

one peice is 220g (60%)

one peice is 180g (40%)


400g x 51% = 204g of copper so...

2 pieces, one 220g and one 180g (220+180=400)

220g x 60% = 132g of copper

180g x 40% = 72g of cooper

132g + 72g = 204g of copper OR 51% of the 400g chunk


Posted by ChemEnhanced on Sep-29-2008 21:48:

so the final piece has 204g of copper and 196 alloy


Posted by cammaxwell on Sep-29-2008 21:49:

quote:
Originally posted by VDub
no...you're reading it wrong...

The 60 and 40% are the copper content of the original 2 pieces...

When they are melted, the resulting piece is 51% copper...


No, I'm not reading it wrong....the answer is above^^^^


Posted by VDub on Sep-29-2008 21:53:

quote:
Originally posted by cammaxwell
400g x 51% = 204g of copper so...

2 pieces, one 220g and one 180g (220+180=400)

220g x 60% = 132g of copper

180g x 40% = 72g of cooper

132g + 72g = 204g of copper OR 51% of the 400g chunk


Yah that seems to work out doesn't it...

But where did you get the 220 and 180?


Posted by ChemEnhanced on Sep-29-2008 21:54:

200.8 and 199.2


Posted by cammaxwell on Sep-29-2008 21:54:

Billy told me...


Posted by VDub on Sep-29-2008 21:55:

quote:
Originally posted by ChemEnhanced
200.8 and 199.2


See????

That's what I got.....


Posted by ChemEnhanced on Sep-29-2008 21:56:

quote:
Originally posted by VDub
See????

That's what I got.....


now look in the back of the math book and get the answer

Copper = 204 Alloy = 196

60%copper (122.4) + 40%alloy (78.4) = 200.8

40%copper (81.6) + 60%alloy(117.6) = 199.2


Posted by cammaxwell on Sep-29-2008 22:03:

quote:
Originally posted by ChemEnhanced
now look in the back of the math book and get the answer

Copper = 204 Alloy = 196

60%copper (122.4) + 40%alloy (78.4) = 200.8

40%copper (81.6) + 60%alloy(117.6) = 199.2


What?

60% of 200.8 is 120.48......not 122.4?

....and 40% of 199.2 is 79.68....NOT 81.6?


Posted by cammaxwell on Sep-29-2008 22:06:

quote:
Originally posted by ChemEnhanced
now look in the back of the math book and get the answer

Copper = 204 Alloy = 196

60%copper (122.4) + 40%alloy (78.4) = 200.8

40%copper (81.6) + 60%alloy(117.6) = 199.2


You guys used the 204g for your calculation, but you have to use the ORIGINAL chuck for that....


Posted by ChemEnhanced on Sep-29-2008 22:09:

quote:
Originally posted by cammaxwell
You guys used the 204g for your calculation, but you have to use the ORIGINAL chuck for that....


I have no idea if I am right....just playing with the numbers provided.


Posted by ChemEnhanced on Sep-29-2008 22:11:

The entire problem is incorrect as you would loose some weight in the melting process....therefore you would also need to determine how much weight is lost in the melting process.


Posted by DigiNut on Sep-29-2008 22:16:

That really depends whether or not Billy is running an industrial assembly line. I mean, it's pretty unlikely that he has the equipment sitting around in his basement to melt and fuse copper with perfect efficiency and without introducing any impurities. So I'd have to assume he's working at a plant somewhere.

Assuming that, we still need to know if it's a clean room, like a fab, or a regular factory where the copper slabs have no doubt picked up all sorts of dirt, and the melting process probably leaves a copper residue behind.

Now, since the question explicitly states "the resulting piece", it also clearly suggests a freezing process. Does it go into a freezer, sealed, or is it just left sitting around until it solidifies? If memory serves, copper doesn't sublimate, but the impurities might at the right atmospheric temperature, which means that the resulting solid might actually be slightly more pure than the original liquid.

Finally, how is the determination of purity being made? It's easy enough to weigh the thing, but in order to determine the purity you usually have to melt it down or distill it, which seems to be a pointless exercise here after making the new alloy. And if Billy had to melt down the original two samples just to find out the purity, how can we be sure that he didn't lose some copper in that process, before he even started combining them? Are we assuming a specific loss rate here or are these ideal, perfect (i.e. imaginary) conditions?

More to the point, if Billy already has a scale, which he would have needed to weigh the final sample, why didn't he just weigh the original two samples in the first place instead of going through all this ridiculous hassle?


Posted by ChemEnhanced on Sep-29-2008 22:21:

quote:
Originally posted by DigiNut
That really depends whether or not Billy is running an industrial assembly line. I mean, it's pretty unlikely that he has the equipment sitting around in his basement to melt and fuse copper with perfect efficiency and without introducing any impurities. So I'd have to assume he's working at a plant somewhere.

Assuming that, we still need to know if it's a clean room, like a fab, or a regular factory where the copper slabs have no doubt picked up all sorts of dirt, and the melting process probably leaves a copper residue behind.

Now, since the question explicitly states "the resulting piece", it also clearly suggests a freezing process. Does it go into a freezer, sealed, or is it just left sitting around until it solidifies? If memory serves, copper doesn't sublimate, but the impurities might at the right atmospheric temperature, which means that the resulting solid might actually be slightly more pure than the original liquid.

Finally, how is the determination of purity being made? It's easy enough to weigh the thing, but in order to determine the purity you usually have to melt it down or distill it, which seems to be a pointless exercise here after making the new alloy. And if Billy had to melt down the original two samples just to find out the purity, how can we be sure that he didn't lose some copper in that process, before he even started combining them? Are we assuming a specific loss rate here or are these ideal, perfect (i.e. imaginary) conditions?

More to the point, if Billy already has a scale, which he would have needed to weigh the final sample, why didn't he just weigh the original two samples in the first place instead of going through all this ridiculous hassle?


I could just imagine some kid at school writing that down on a test because he didn't know the answer.


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