SOLUTION: can someone please help me with this problem: A certain radioactive isotope decays at a rate of 0.25% annually. Determine the half - life of this isotope, to the nearest year.

Question 163533: can someone please help me with this problem:
A certain radioactive isotope decays at a rate of 0.25% annually. Determine the half - life of this isotope, to the nearest year.
a. 120 years
b. 277 years
c. 200 years
d. 3 years
Answer by Fombitz(32388) (Show Source): You can put this solution on YOUR website!
The isotope follows this power law as a function of time,

where t is measured in years and is the initial amount of the isotope.
Half life is when ,

.
.
.
Looks like b) 277 years is the closest answer.
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