Posted by **Val** on Sunday, March 28, 2010 at 9:00pm.

Gallium65, a radioactive isotope of gallium, decays by first order-kinetics. The half-life of this isotope is 15.2 min. How long would it take for 7/8 of a sample of this isotope to decay?

15.2 min

30.4 min

45.6 min

48.0 min

I'm not sure how to do this. I initially tried by finding k for the values given for the half life (ln2/15.2 min=k) and hten used k to find the value for when 7/8 was left over, but I keep getting t= 2.9 minutes which isn't right.

having trouble posting so I'm doing these in parts..

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