1) The model that fulfills this description is the one that resembles the exponential model "half-life"
2) So we can write out the following considering that year after year her hopes go half:
[tex]\begin{gathered} N(t)=N_0(\frac{1}{2})^t \\ Testing: \\ N(0)=100(\frac{1}{2})^0\Rightarrow N(0)=100 \\ N(1)=100(\frac{1}{2})^1\Rightarrow N(1)=50 \\ N(2)=100(\frac{1}{2})^2\Rightarrow N(2)=25 \end{gathered}[/tex]Note that when we test, we can see the number decreasing to half it was in the last year.