Quote (RzChaos @ Mar 12 2016 06:12pm)
You don't need an actual function.
SAT scores are declining --> Implies that the first derivative is negative.
The rate at which they are declining is decreasing --> Implies that the second derivative is positive. This one may be less intuitive. At first they are declining quickly, so the first derivative at t = x is "very negative", but they stop declining as quickly as time goes on, so the first derivative at t = X + Y is "less negative". The first derivative graph is increasing, so the second derivative is positive.
If you really want to, you can just model the sat scores as something like
Score(t) = 2000 - 100sqrt(t)
Ok good, I was thinkin that but wasn't 100% sure. Thank you a ton for the help!