Question 1180052
.


            It is a good question to check if a person knows the subject.


            @mananth gave you INCORRECT answer, so he definitely did not pass the test.


            See my correct solution below.



<pre>
Since we are given that the half-life is of 10 years, we can write the decay equation in this form


    m(t) = {{{20*(1/2)^(t/10)}}},


where t is the time in years; m(t) is the remaining mass; 20 is the starting mass of 20 grams.


To answer the problem's question, substitute t = 5 into the formula.  Yoiu will get


    m(5) = {{{20*(1/2)^(5/10)}}} = {{{20*(1/2)^(1/2)}}} = {{{20/sqrt(2)}}} = {{{(20*sqrt(2))/2}}} = {{{10*sqrt(2)}}} = 10*1.414.. = 14.14 grams  (rounded).


<U>ANSWER</U>.  14.14 grams remained after 5 years.
</pre>

Solved  &nbsp;&nbsp;&nbsp;&nbsp;(correctly).


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Again, &nbsp;if a person does not know the subject firmly or is in hurry to answer the question,

he &nbsp;(or she) &nbsp;can easily make a &nbsp;FATAL &nbsp;MISTAKE &nbsp;answering such question.


A dose of accuracy and expert knowledge is required . . . 



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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.



&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Use this lesson as your handbook, &nbsp;textbook, &nbsp;guide, &nbsp;tutorials, and &nbsp;(free of charge) &nbsp;home teacher.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Learn the subject from there once and for all.



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
https://www.algebra.com/algebra/homework/quadratic/lessons/ALGEBRA-I-YOUR-ONLINE-TEXTBOOK.lesson


to your archive and use it when it is needed.