The algebra you refer to is to get a PPM concentration. That's a simple linear value: 1,000,000 PPM is 100%, 500,000 PPM is 50%, so 1,000,000 is 2x 500,000 is 5x 100,000. Linear.
Then you multiply that value by an integer, not a function. So it's still a linear equation. Try graphing it, you'll...