There are many techniques you can use to change a decimal to a fraction. The easiest way is to just go to math and then fraction on your graphing calculator, however, it is also possible to change decimals to fractions by hand.
First: Put the decimal over 1 in a fraction.
Second: Multiply both top and bottom by 10 for every number after the decimal point. Like, if there are two numbers after the decimal point, then use 100, if there are three then use 1000, and so on.
Lastly: Simplify your fraction.
For example, say you are given the decimal .50
You would then put that decimal over 1
So now you have .5/1
Now multiply the top and bottom numbers of your fraction by 100
So now you have 50/100, which you then simplify to 1/2. This is your final answer!