Question 1199030
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One full day is 24 hours.


24 hours is  how many half-lives ? - It is  {{{24/8.5}}} = 2.82 half-lives, i.e. close to 3 half-lives.


Hence, after 24 hours, the remaining amount will be  about  {{{1/2^3}}} = {{{1/8}}}  of the initial amount, which is 20 ounces.


So, we can expect  something about {{{20/8}}} = 2.5 ounces for remaining mass.


The closest option is D).    <U>ANSWER</U>


All other optional masses are much lesser and much further in time than 3 half-lives; 
so, this MENTAL estimation is just enough to make a final conclusion.
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Solved.