Math Help Needed!!

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

  1. touchher macrumors regular

    Nov 23, 2007
    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


    Jan 31, 2005
    Omaha, NE, USA
    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
  3. touchher thread starter macrumors regular

    Nov 23, 2007
  4. nakamuramori2 macrumors regular

    Aug 14, 2008
    woo... cant think anything... is this for GMAT math??
  5. Schtumple macrumors 601


    Jun 13, 2007
    Are you superman??? How in gods name did you work that out????
  6. BigHungry04 macrumors 6502

    Mar 14, 2008
  7. ChrisA macrumors G4

    Jan 5, 2006
    Redondo Beach, California
    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.

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