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Math Help - Using a Regression Equation

  1. #1
    Junior Member
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    Using a Regression Equation

    I have to find the half-life of Iodine-129 using the regression equatioon

    y=100e^-0.153x

    The chart I was given is divided into age (billions of years) and % of original II-129:

    2.0 (74%), 3.5 (59), 4.2 (53%), 4.3 (52%)

    I know that to find the half-life I have to find the value of x. However, I am not sure how to do this. Could you help? Thanks.
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  2. #2
    Senior Member Twig's Avatar
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    To solve for half-life,
    you see that 100 is starting value when x=0.
    So, 100 \cdot e^{-0.153x} = 50

     x = \frac{ln(\frac{1}{2})}{-0.153} \approx 4.53
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