chemistry
posted by L .
Radioactive materials are often used in biological studies. A radiation biologist studies the rate of decomposition of a certain substance and obtains the following data:
Time(days) 0 4.0 8.0 12.0 16.0
Mass (μg) 15.50 10.90 7.67 5.39 3.79
Determine the rate constant in units of day^(1).

chemistry 
DrBob222
I would do this.
ln(No/N) = kt
No = what you started with.
N = what you ended up with.
k = what you're looking for.
t = time = 4 days
I would plug in all the data, find k for each 4 day period, then average all of the values of k together.
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