Chemistry
posted by tina .
If 30% of a sample of radioactive isotope decays in 24 hrs, what is the halflife?
How do i know which order to use? and do I convert hr to mins or seconds?
Pls help for my exam tomorrrow

Chemistry 
DrBob222
ALL radioactive decay problems are first order so you use ln(No/N) = kt.
If you want the half life in hours, leave it as is. If you want it in min or seconds, then convert the 24 hours to some other unit. Since the problem doesn't specify, I would leave it as 24 hours. 
Chemistry 
Anonymous
In n=kt +in,no
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