A zoologist is investigating the growth of a population of red squirrels in a forest - AQA - A-Level Maths Mechanics - Question 2 - 2017 - Paper 2

To find the size of the squirrel population at the start of the investigation, we need to evaluate the equation at $t = 0$.

Substituting $t = 0$ into the equation:

$N = \frac{200}{1 + 9e^{-0.5 \cdot 0}}$

This simplifies to:

$N = \frac{200}{1 + 9e^{0}}$

Further simplifying, since $e^{0} = 1$:

$N = \frac{200}{1 + 9 \cdot 1} = \frac{200}{10} = 20.$

Therefore, the size of the squirrel population at the start of the investigation is 20, which should be circled in the provided options.