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?

- calculus -
**Reiny**, Thursday, February 17, 2011 at 5:36pm
can you solve

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

- calculus -
**Melody**, Thursday, February 17, 2011 at 5:48pm
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?

- calculus -
**Reiny**, Thursday, February 17, 2011 at 5:53pm
correct, good job.

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