A) 1080
B) 2430
C) 3240
D) 4860
Correct Answer: A
Solution :
\[\lambda ={{\lambda }_{1}}+{{\lambda }_{2}}\Rightarrow \frac{1}{T}=\frac{1}{{{T}_{1}}}+\frac{1}{{{T}_{2}}}\] \[\therefore T=\frac{{{T}_{1}}{{T}_{2}}}{{{T}_{1}}+{{T}_{2}}}=\frac{810\times 1620}{810+1620}=540\ years\] Hence \[\frac{1}{4}\]th of material remain after 1080 years.
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