Answer:
Given:
Initial mass = 18 g
k-value = 0.1226
The mass at time t (days) is
At half life, m = 18/2 = 9 g.
The time for half life is given by
Therefore
ln(1/2) = -0.1226t
Hence obtain
t = ln(1/2) / -0.1226
= 5.654 days
Answer: 5.7 days (nearest tenth)
or
For this problem, we use the formula for radioactive decay which is expressed as follows:
An = Aoe^-kt
where An is the amount left after time t, Ao is the initial amount and k is a constant.
We calculate as follows:
A0 = 18
An = 18/2 = 9
k = 0.125
9 = 18 e^-0.125t
0.5 = e^-0.125t
t = 5.55 days