Question

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?

Answer 1

can you solve

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

Answer 2

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?

Answer 3

correct, good job.