Question 1145226
.
<pre>

(a)  23 years is twice half-life period --- therefore,   {{{(1/2)^2}}} = {{{1/4}}} of the substance will remain after 23 years.


(b)  34.5 years is thrice half-life period --- therefore,  {{{(1/2)^3}}} = {{{1/8}}} of the substance will remain after 34.5 years.
</pre>