a) Separate variables correctly and integrate of at least one side

Carry out an attempt to find $A$ and $B$ such that $\frac{1}{{N\left( {1800 - N} \right)}} \equiv \frac{A}{N} + \frac{B}{{1800 - N}}$, or equivalent

Obtain $\frac{2}{N} + \frac{2}{{1800 - N}}$ or equivalent

Integrates to produce two terms involving natural logarithms

Obtain $2{\text{ }}ln{\text{ }}N - 2{\text{ }}ln{\text{ }}\left( {1800 - N} \right) = t$ or equivalent

Evaluate a constant, or use $N = 300$ and $t = 0$ in a solution involving $\alpha {\text{ }}ln{\text{ }}N$, $b{\text{ }}ln\left( {1800} \right)$ and $ct$

Obtain $2{\text{ }}ln{\text{ }}N - 2{\text{ }}ln{\text{ }}\left( {1800 - N} \right) = t - 2{\text{ }}ln{\text{ }}5$ or equivalent

Use laws of logarithms to remove logarithms

Obtain $N = \frac{{1800{e^{\frac{1}{2}t}}}}{{5 + {e^{\frac{1}{2}t}}}}$ or equivalent

b) State or imply that $N$ approaches $1800$