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Math Help - radioactive decay word problem

  1. #1
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    After t years, 50e^{-0.015t} pounds of a deposit of a radioactive substance remain. The average amount per year not lost by radioactive decay during the second hundred years is
    (A) 2.9 lb
    (B) 5.8 lb
    (C) 7.4 lb
    (D) 11.1 lb
    (E) none of these

    if it helps the answer is B but i need help how to get that answer
    Last edited by mr fantastic; April 28th 2010 at 06:55 PM. Reason: Merged posts
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by yoman360 View Post
    After t years, 50e^{-0.015t} pounds of a deposit of a radioactive substance remain. The average amount per year not lost by radioactive decay during the second hundred years is
    (A) 2.9 lb
    (B) 5.8 lb
    (C) 7.4 lb
    (D) 11.1 lb
    (E) none of these

    if it helps the answer is B but i need help how to get that answer
    The mass remaining at time t is:

    m(t)=50e^{-0.015t}

    The amount lost between t_1 and t_2 is:

    M(t_1,t_2)=m(t_1)-m(t_2)

    So the average loss per year is:

    A(t_1,t_2)=M(t_1,t_2)/(t_2-t_1)

    CB
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