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posted by Melody on Thursday, February 17, 2011 at 3:18pm.

How do I set-up/solve this problem? Please help me. The half-life of the radioactive isotope gallium-70 is 20 minutes. If the initial amount of gallium-70 is 25 milligrams, when will 10 milligrams be left?

can you solve 10 = 25(.5)^(t/20) where t will be in minutes ?

This is what I got.. 25(1/2)^(t/20)=10 (1/2)^(t/20)=10/25=2/5 (1/2)^(t/20)=2/5 t/20=log(2/5)/log(1/2) t=20(log(2/5)/log(1/2)) t=26.44 Is this correct?

correct, good job.

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