1.
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:
An = Aoe^-kt
0.5 = e^-k(1.4x10^10)
k = 4.95x10^-11
An = Aoe^-kt
25 = Aoe^-4.95x10^-11(2.8x10^10)
Ao = 100 g
