Strange Growth Formula Needed!

[Gathon.zypher]

Alright - here's my problem: I need to have a formula where when 0<X<11, it's multiplied by three. So 3X would simply be 9. Now it starts to get tricky. For every 10 after that, X is equal to the last value plus one. So 10X=30, but 11X=34. After another 10, X will equal 5 (21X=75), and then in another 10, it's worth 6.

So...
The numbers are starting to eat my brains, and if I don't have a formula for this strange growth situation, I will lose the last little bit of my neurons. Thank you so much for your help.

Brent

Edit: The closest I've gotten so far is 2X+1/10X^2

[stapel_eliz]

If the behavior changes, wouldn't the formula also need to change? This sounds like you need a piecewise function, not a rational function. Also, the rational function you have proposed does not appear to work for either half...?

[Gathon.zypher]

Did I mention that I'm a math noob? No idea what the difference is between a piecewise function and a rational function. I'll look it up, so thank you for the start on where to go with this.