The amount of a certain radioactive element in a sample is d

The amount of a certain radioactive element in a sample is decreasing exponentially at a a rate of 1.5% per year. In what year will the amount of that radioactive element left in the sample he 60% of what it was in 2012?

Solution

N(t) = Noe^-kt

k = 0.015 ; N(t) = 0.6No

So, 0.6No = Noe^-0.015t

0.6 = e^-0.015t

t = -ln0.6/0.015 = 34.05

Since the year 2012 it would be 2047