if 60% of a radioactive element remains radioactive after 300 million years, then what percent remains radioactive after 500 million years? what is the half-life of this element?

Answer 1

m = M e^-kt
m/M = 0.60 = e^-k(300)
ln 0.60 = -300 k
-.511 = -300 k
k = 0.00170/million years

m/M = e^-0.00170(500)
= 0 .427
so
42.7 %

for half life
0.5 = e^-.00170 t
ln .5 = -.0017 t
solve for t in millions of years