Question
Half-life of a radioactive substance is 10 days. The
time after which only 1/16th of it remains is:Solution
The substance reduces to 1/2 every 10 days. 
Time = n x Half-life Given: Half-life = 10 days Final amount = 1/16 of original 
Thus, Time = n x Half-life = 4. 10 = 40 days
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