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Math Help - exponential word problem

  1. #1
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    exponential word problem

    Can someone please help me with part b and c.
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  2. #2
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    Quote Originally Posted by Tweety View Post
    Can someone please help me with part b and c.
    to a)

    Plug in D = 10 and t = 5. Use a calculator. I've got x \approx 5.353\ \rm{mg}

    to b)

    Now D = 10 + 5.353 and t = 1. Use a calculator. I've got x \approx 13.54897\ \rm{mg}

    to c)

    Solve the equation for t:

    3 = 15.353\cdot e^{-\frac18 t}~\implies~\dfrac{3}{15.353} = e^{-\frac18 t}

    Use logarithm:

    \ln\left(\dfrac{3}{15.353} \right) = -\frac18 t

    I'll leave the rest for you.
    Spoiler:
    I've got t \approx 13.06\ h, that means nearly 13 hours and 4 minutes
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  3. #3
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    Thank you,

    but D= the amount of dose given, so why have you added the answer to part 'a' , which is the amount of the drug in the bloodstream?

    Cause I thought to put D = 20,
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  4. #4
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    Quote Originally Posted by Tweety View Post
    Thank you,

    but D= the amount of dose given, so why have you added the answer to part 'a' , which is the amount of the drug in the bloodstream?

    Cause I thought to put D = 20,
    The text of b) reads: A second dose is given after 5 hours.

    From a) I know the amount of the drug after 5 hours and to this amount a second dose is added.
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