Initial stuff? 'A school of fish is reducing such that...'

[ChaosTheory]

I'm having a really hard time with these questions and this one is driving me around in circles so any help would be greatly appreciated

A school of fish is reducing in number such that the rate of change is proportional to the number of fish at any particular time. After two years there are 100 fish and after 3 years there are 50 fish left. Find The initial population.

I need help on just where to start and how to approach this type of question because I'm not sure how. Thanks

 

[morson]

Let the number of fish at any time be y. Translate what is said into a mathematical (or more specifically, a differential) equation:

\(\displaystyle \frac{dy}{dt}\ = -ky\), an exponential relationship (note the negative in the equation, indicating that the population is decreasing).

Solve this differential equation. If you're not sure, you should check up on first order differential equations.