Question 1180948
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3. A sample of a radioactive isotope was found to be 40 mg 18 days ago and 5 mg today.
a) What is the half-life of the substance?
b) How many milligrams of the substance will be left 12 days from today?
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<pre>
(a)  The ratio of the current mass to the initial mass is  {{{5/40}}} = {{{1/8}}} = {{{1/2^3}}}.


     It means that 3 (three) half-lives passed from the beginning to the current moment.


     It means that 18 days comprize 3 half-lives.  Hence, one half-life is {{{18/3}}} = 6 days.     <U>ANSWER</U>




(b)  12 days from today comprise  12/6 = 2 half-lives;

     So, in 12 days after today, the remaining mass will be  {{{5*(1/2^2)}}} = {{{5/4}}} = 1.25 milligrams.    <U>ANSWER</U>
</pre>

Solved.  &nbsp;&nbsp;&nbsp;&nbsp;//  &nbsp;&nbsp;&nbsp;&nbsp;All questions are answered.


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On radioactive decay, &nbsp;see the lesson

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=https://www.algebra.com/algebra/homework/logarithm/Radioactive-decay-problems.lesson>Radioactive decay problems</A> 

in this site.


You will find many similar &nbsp;(and different) &nbsp;solved problems there.



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Also, &nbsp;you have this free of charge online textbook in &nbsp;ALGEBRA-I &nbsp;in this site

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=https://www.algebra.com/algebra/homework/quadratic/lessons/ALGEBRA-I-YOUR-ONLINE-TEXTBOOK.lesson>ALGEBRA-I - YOUR ONLINE TEXTBOOK</A>.


The referred lesson is the part of this online textbook under the topic "<U>Logarithms</U>".



Save the link to this online textbook together with its description


Free of charge online textbook in ALGEBRA-I
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