i’ve been asked for help to translate the OE expression fīfte healf hund. numerals can be tricky! for example, in old germanic (especially ON) the word for ‘hundred’ often does not mean 100 but 120 (!), the so called Grosshundert, which is, by the way, not to be confused with the gros, which is 12 * 12 = 144). another example of odd counting are the danish numerals partly based on a vigesimal system and – surprisingly – still in use today.
to find the correct translation for fīfte healf hund, i looked through the entry for ‘healf’ in the bosworth/toller dictionary , and among some weird stuff i found the following two clear OE/Latin translation pairs that should allow to come to a certain conclusion:
ðridda half haga = duas possessiunculas et tertiam dimedia
fīfte healf hund = quadringenti et quinquaginta
the first example means something along the lines of ‘two and a half residences’, and the second case is clearly 450.
the correct way to read the phrase is therefore: “fīfte healf” = 4.5, and then times 100, with the result 450.
 Bosworth, J. & Toller, T. N.: An Anglo-Saxon Dictionary. Oxford 1898. 2 volumes.