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Homework Help: math

Posted by Jackie on Friday, January 25, 2013 at 11:43am.

assume the substance has a half-life of 11 years and the initial amount is 126 grams.How long will it be until only 15 % remains?

• math - Damon, Friday, January 25, 2013 at 11:52am

  1/2 = e^k(11)
  ln .5 = 11 k
  11 k = -.5978
  k = -.05435
  so
  .15 = e^-.05435 t
  -1.897 = - .05435 t
  t = 34.9 years
  

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