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Thread: how to solve simple half life? ( gr9 mathematics)?

  1. #1
    Join Date
    Aug 2007
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    Default how to solve simple half life? ( gr9 mathematics)?

    Hey there,

    Im studying for math exams (gr9) and I have a half-life question that wasnt taught to me. I did some reading on it and this is what i have so far

    Amount left=Amount original(1/2) * time/time half life.

    This is my problem : In 30h, a sample solution of plutonium-243 decays to 1/64 of its original amount. Determine the half life of each isottope.

    Thanks in advance.

    PS:and how would i simply finf the Amount left with all the given required values.

  2. #2
    Join Date
    Aug 2007
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    After one half life, you have 1/2 left.
    After two half lives, you have 1/4 left.
    After three half lives, you have 1/8 left.
    After four half lives, you have 1/16 left. (etc. etc.)

    Your problem has only 1/64 left. 1/64 is 1/2 to the sixth power. (.5*.5*.5*.5*.5*.5). That means that six half lives have passed.

    Since it took 30 hours for six half lives to pass, each half life is (30/6) five hours long.

  3. #3
    Join Date
    Aug 2007
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    m(t)=m(0)(1/2)^t/T, T half life.
    m(t)///////////M(0)=1/64, t=30hours
    1/64=(1/2)^30/T
    (1/2)^6=(1/2)^30/T
    30/T=6, T=5 hours.

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