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easy half life problem i can't do!

Discussion in 'DAT Discussions' started by msu08, Dec 29, 2008.

  1. msu08

    7+ Year Member

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    If the half-life of an isotopic nuclide is 24 hours, how long will it take for 75% of the sample to decay?



    A. 12 hours
    B. 24 hours
    C. 36 hours
    D. 48 hours
    E. 60 hours

    The answer is 48... i got 36..anyone understand this problem?
     
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  3. zuma35

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    Start with 100g. After 24 hours 50g remains. After 48 hours (another half life of 24 hours), 25g remains.
     
  4. montag925

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    any halflife problem that I ever reviewed or did on the DAT the two times that I took it did not require any equation, but rather only common sense and reasoning as in this one.
     
  5. joonkimdds

    joonkimdds Senior Member
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    I know exactly what mistake u r making. U skipped 1 step.
    U r going directly from 100% to 25%.
    Just like a math problem.
    0 ==> 50 miles takes 24 hrs.
    how long will it take for u to go from 0 to 75 mile and answer would be 36 hrs.
    But that's not the way to solve this problem.
    Above method is assuming that ur speed never change.
    but think about a crappy car that slows down speed in half after half life :D
     

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