math/algebra
posted by Monica .
Use the exponential decay equation, to find the halflife of a material that decays from 40mg to 30mg in 10 hours.

30 = 40e^10k
.75 = e^10k
10k = ln.75
k = ln.75/10 = .028768
then
1/2 = e^.028768t
 .028768t = ln .5
t = ln .5/.028768 = 24.09
the halflife is appr. 24.1 hours