What is 3.008 3.825 3.09 and 3.18 ordered from greatest to least?

Well lets look here at something.
Tenths are the greatest compared to hundredths or thousandths.
So if that is the case We can tell that 3.008 is the least since it only has one value on the end in the thousandths place (all are 3.??? which is why this stays true)
Tenths place > 0.000 (The First 0)
Hundredths place > 0.000 (Second 0)
Thousandths place > 0.000 (Third 0)
Look for the greater values in all of these. Remember tenths is greater than hundredths and hundredths to thousandths. 
So we can order it properly > 3.825, 3.18, 3.09, 3.008