msu08

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Nov 14, 2006
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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?
 

zuma35

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Sep 6, 2008
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Start with 100g. After 24 hours 50g remains. After 48 hours (another half life of 24 hours), 25g remains.
 

montag925

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Dec 29, 2006
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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.
 

joonkimdds

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Jun 30, 2005
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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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