1.1. The number of cases of an unknown virus are modelled by the formula

$V=\frac{625}{{(d-25)}^{2}}$          $0\leqd<25$

where $d$ is the number of days after the first case was discovered and $V$ is the total number of cases to date.

Sketch a graph of $V$against $d$, clearly marking the coordinate where the graph intersects the $V$-axis.

1.2. Explain why the model is not appropriate for $d\geq25$.

1.3. Scientists suggest the model is not accurate after 18 days. Suggest a reason why.

1.4. The model is a graph transformation of the graph with equation $y=\frac{a}{{x}^{2}}$, where $a=625$. Describe this transformation.