I agree I would prefer not to convert to fractions as it seems to make things more complicated. But if we just say add trailing zeros until they have the same length that seems a bit like an arbitrary rule unless we can explain the logic. I was basing the hints on a Common Core document which talked about understand, say 0.12 is 12 hundredths. Maybe writing it out in words would be easier that showing the fractions (although we would then have to deal with ten thousandths, which seems a bit ugly).