1/20, 2/3, and 20/25 do not have a whole number that could fit in them when 5/4 does (1 1/4) so when all the other fractions can't have a whole number fit in, 5/4 or 1 1/4 does.
Out of the given options, is the only fraction that is improper. All other options are not improper. Therefore, would not belong is the given group of fractions.