Question 1171696
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Paracetamol is a drug used to treat mild to moderate pain and to reduce fever. It has a half-life in the body of 3 hours. 
Under a Doctor's care, patient N is given a dose of a certain paracetamol. Patient N asks the doctor for another same dose 
of this paracetamol. The doctor agrees to allow patient N to take dose once there is only 6.25% of the original dose 
remaining in the body. How long will patient N have to wait, before taking another dose of this paracetamol?
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Notice that   6.25%   is  this ratio   {{{6.25/100}}} = {{{1/16}}} = {{{1/2^4}}}.


It means that after  4  (four)  half-life periods the amount of the drug in the body will reach  6.25%  of the original level.


So, &nbsp;the &nbsp;<U>ANSWER</U> &nbsp;to the problem's question is  &nbsp;4 &nbsp;times half-life period, &nbsp;or &nbsp;4 x 3 hours = 12 hours.


You do not need to make long unnecessary calculations to answer the problem's question.