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How much of a radioactive kind of copper will be left after 39 hours if you start with 64 grams and the half-life is 13 hours?

 Feb 3, 2021
 #1
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39 hours is 3 half lives

64 * 1/2 * 1/2 * 1/2 =   69 * 1/8 = ....... grams left

 Feb 4, 2021
 #2
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The "9" in 69 * 1/8 is a typo.   The guest actually meant 64 * 1/8.  

 

64 grams with a half life of 13 hours  

 

After the 1st 13 hours there's 32 grams left  

After the 2nd 13 hours there's 16 grams left  

After the 3rd 13 hours there's 8 grams left  

Guest Feb 4, 2021

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