All you have to do is do this:
pretend its: 0.8
0.8 = 8/10 which can be simplified into 4/5.
So like if its: 0.18
0.18 = 18/100 which can be simplified...somehow...I'm too lazy
0.188 = 188/1000 then simplify that.
So all you have to do is see if its in the tenths, hundredths, or thousandths place and just make it a fraction like that.
Hope I Helped!!!!