I am trying to create a scoring scale for a game. I want the scale to be non-linear to reflect the realness of the game. The score is determined by time, the less time you take, the greater score you get.
If you take more than $5$ minutes to complete the challenge, your score is $0.$
If you take $0$ seconds to complete the challenge, your score is $40.$
My current equation is linear: $y = {\rm MAX\ SCORE} - \frac{{\rm MAX\ SCORE}}{{\rm TIME\ TO\ MIN\ SCORE}}\times {\rm time}$
However, I want the score to accelerate more quickly towards $40$ the closer you get to 0. What equation can I use to do this?