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

    swiftaw

    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
     
  3. touchher thread starter macrumors regular

    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

    Schtumple

    Joined:
    Jun 13, 2007
    Location:
    benkadams.com
    #5
    Are you superman??? How in gods name did you work that out????
     
  6. BigHungry04 macrumors 6502

    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.
     

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