# Math Help Needed!!

Discussion in 'Community Discussion' started by touchher, Sep 7, 2008.

1. ### touchher macrumors regular

Joined:
Nov 23, 2007
#1
I don't understand how to do these problems/ set it up. Any help would be greatly appreciated. Answer is 18g.

a jeweler has five rings, each weighing 18 g, made of an alloy of 10% silver and 90% gold. he decided to melt down the rings and add enough silver to reduce the gold content to 75%. how much silve should he add?

2. ### swiftaw macrumors 603

Joined:
Jan 31, 2005
Location:
Omaha, NE, USA
#2
Okay, 5 rings each 18g, so total weight is 5*18 = 90g

Now, they are 10% silver and 90% gold, so 9g of silver and 81g of gold.

Want to add silver, until gold content is 75%. Thus, let's suppose the amount needed to be added is x.

So then there will be (9+x)g of silver, 81g of gold for a total weight of (90+x)g

Gold needs to be 75% of the total, so we know that 81/(90+x) = 0.75

Re-arranging the final equation, gives us 81 = 0.75*(90+x)
Therefore 81 = 67.5 + 0.75x, or 0.75x = 13.5, or x = 18g

So 18g of silver needs to be added

Joined:
Nov 23, 2007
4. ### nakamuramori2 macrumors regular

Joined:
Aug 14, 2008
#4
woo... cant think anything... is this for GMAT math??

5. ### Schtumple macrumors 601

Joined:
Jun 13, 2007
Location:
#5
Are you superman??? How in gods name did you work that out????

Joined:
Mar 14, 2008
Location:
Connecticut
7. ### ChrisA macrumors G4

Joined:
Jan 5, 2006
Location:
Redondo Beach, California
#7
Come on now, this is 8th grade level work, introductory algebra.
Now maybe we can all complain how basic math and science education has gone down hill.