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Math Help - Half-Life calculation

  1. #1
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    Half-Life calculation

    Radioactive carbon decays exponentially with a half-life of 5,780 years. Determine how long ago a sample of carbon began to decay if there is now 5% of it left.

    I'm not sure how to get started to all help is appreciated!
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  2. #2
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    Let A= the amount of radioactive material remaining at anytime t, you have the following information

    Use the following A = A_0e^{kt}

    at t=0, A = A_0 and t=5780, A = \frac{A_0}{2}

    this will help you solve for k.

    After this solve for t when A = 0.05\times A_0
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