A) 3.8 days
B) 16.5 days
C) 33 days
D) 76 days
Correct Answer: B
Solution :
By the formula \[N={{N}_{0}}{{e}^{-\lambda t}}\] Given \[\frac{N}{{{N}_{0}}}=\frac{1}{20}\]and \[\lambda =\frac{0.6931}{3.8}\] Þ \[20={{e}^{\frac{0.6931\times t}{3.8}}}\] Taking log of both sides or log 20 \[=\frac{0.6931\times t}{3.8}{{\log }_{10}}e\] or 1.3010\[=\frac{0.6931\times t\times 0.4343}{3.8}\] Þ \[t=16.5\]days.
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