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Homework Help: Find the percentage increase in y

  1. Nov 5, 2006 #1
    y is directly proportional to x2.
    x is increased by 100%.
    Find the percentage increase in y.

    y=k x2

    y= k (100 + x2)
    then i went to find the k,
    which is
    k= y/ (100 + x2)

    so i put back the k which i found into y= k (100 + x2)
    which is :
    y= y/(100 + x2) (100 + x2)

    them im stuck here..:yuck:
    somebody pls helppp!
    thanks lotsa.:smile:
  2. jcsd
  3. Nov 5, 2006 #2
    it should be [tex] 4x^{2} [/tex] not [tex] x^{2} + 100 [/tex]
    Last edited: Nov 5, 2006
  4. Nov 5, 2006 #3


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    Homework Helper

    x is increased by 100% just means that x has been doubled (i.e: 2x), and not 100 + x. Do you see why?
    Consider the original amount (say b) to be 100%, so when increasing the original amount (i.e increase b) by 100% means that you add one more b to your original b, and get 2b, right?
    So, can you go from here? :)
    @courtrigrad: No, it should be 4x2, not 2x2. :smile:
    EDIT: He did edit the post. Cheers. :)
    Last edited: Nov 5, 2006
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