How to interpret a range from 0 to 600 to a range between 1 to 0

Question

Sorry for the poor wording, I'm not sure how to describe this.

As the value $x$ increases from $0$ to $600$, how can I make the value $y$ to range from $1$ to $0$. So for example, when $x = 0$, $y = 1$, and when $x=600$, $y = 0$ (and if $x=300$ then $y = 0.5$, and so on.) Any pointers in the right direction would be helpful.

Answer 1

There might be many ways to achieve this, here's one:

Define $y = 1 - \frac{x}{600}$

Answer 2

Find the equation of the line through the points (0,1) and (600,0).

In this case, if a line has $x$-intercept $a$ and $y$-intercept $b$, then the equation of the line is

$$\frac xa + \frac yb = 1$$

In your case this would be

$$\frac{x}{600} + \frac y1 = 1$$

$$x + 600y = 600$$

$$y = 1 - \frac{1}{600}x $$