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Radioactive Decay?

  1. Jan 27, 2010 #1
    I am confused about the half life and radioactive decay and how to figure out the problems.

    here is one from my book:

    A zircon sample contains 4000 atoms of the radioactive element 235U. Given that 235U has a half life of 700 million years, how long would it take to decay to 125 atoms?
  2. jcsd
  3. Jan 28, 2010 #2
    smells like homework
  4. Jan 30, 2010 #3
    it is simple!
    Just get the formula for radioactivity..and substitute all the number that you..
    tip any physics books with a topic 'radioactivity' or google 'decay law'
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