A) 9 years
B) 8 years
C) 6 years
D) 24 years
Correct Answer: A
Solution :
By formula \[N={{N}_{0}}{{\left( \frac{1}{2} \right)}^{t/T}}\]or \[{{10}^{4}}=8\times {{10}^{4}}{{\left( \frac{1}{2} \right)}^{t/3}}\] or \[\left( \frac{1}{8} \right)={{\left( \frac{1}{2} \right)}^{t/3}}\]or \[{{\left( \frac{1}{2} \right)}^{3}}={{\left( \frac{1}{2} \right)}^{t/3}}\,\,\Rightarrow 3=\frac{t}{3}\] Hence t = 9 years.
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