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Homework Help: Half life problem

  1. Dec 13, 2009 #1
    1. Half life of a radioactive substance is 13 days. How long for 400 grams to decay to 300 grams? Solve algebraically and show all work. Give both exact answers and the answer rounded to 4 decimal places.

    So I manipulated (1/2)A0=A0e13K to obtain K = ln(1/2)/13

    Where do I go from here?
  2. jcsd
  3. Dec 13, 2009 #2


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    Put your known numbers back in the equation:

    A = A0e(kt)
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