What is one way you could compare decimal numbers of different lengths?

What do you mean?.. Do you mean: e.g. How many tens are in 12.476? So you basically have the 70 as ten right? Well you need to count from the first number (12). So the answer to that example would be 1247. Forget about the decimal point.

You can add placeholders to make them all the same length. A placeholder is always 0.
For example if i wanted to order the numbers below:
5.12
5.6
5.2457
5.238
I would add 0's to make them all the same length as the longest:
5.1200
5.6000
5.2457
5.2380
Now it is easier to order them:
5.12
5.238
5.2457
5.6
Just make sure when you write the answer at the end you take off the extra 0's because sometimes leaving placeholders on might mark you down.
Hope this helps :)

Aquadratic function is one of the form f(x)=ax2 + bx + c l, where a,b, and c are numbers with are not equal to zero.