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For my next trick, I want to do the same thing I did with -fun but with -kyaku, the number turned suffix that means 100. You’ll quickly notice that the pattern is not at all the same. It looks like it should be simpler, but in fact is a bit more intricate.
Let’s look at the set:
Here we have three variations on the single suffix “hyaku.”
hyaku (2, 4, 5, 7, 8, 9)
ppyaku (6, 8)
One can make a silly mathematical rule for this: If the base number is divisible by 24 and is even, it takes “ppyaku,” otherwise, it takes “byaku.”
But we can do better.
The Hundred Rule
Let’s begin with the base set
Ichi* (does not apply in this sequence)
1) If the main lexeme ends in an unrounded vowel + a nasal, then it takes the “byaku” variation.
Ni –> (does not end in a nasal, n/a, ×)
San –> sanbyaku (DONE)
Yon –> (ends in a nasal, but not in an unrounded vowel, n/a, ×)
Go –> (does not end in a nasal, n/a, ×)
Roku –> (does not end in a nasal, n/a, ×)
Nana –> (does not end in a nasal, n/a, ×)
Hachi –> (does not end in a nasal, n/a, ×)
Kyuu –> (does not end in a nasal, n/a, ×)
2) ONLY for only those main lexemes with more than one syllable, drop the unvoiced consonants in non-initial position (here in bold). ONLY IF the vowels are adjacent and NOT identical, drop the second and add “ppyaku”
Ni –> (Only one syllable, n/a, ×)
Yon –> (Only one syllable, n/a, ×) [Two morae, one syllable]
Go –> (Only one syllable, n/a, ×)
Roku –> Rou (Vowels are adjacent and not identical, second is dropped) –> roppyaku (DONE)
Nana –> (Vowels are not adjacent and are identical, n/a, ×)
Hachi –> Hai (Vowels are adjacent and not identical, second is dropped) –> Happyaku (DONE)
Kyuu –> (Only one syllable, n/a, ×) [Two morae, one syllable]
3) Everything else stays the same and receives the “hyaku” variation.
Ni –> Nihyaku (DONE)
San –>Sanbyaku (DONE) [Step 1]
Yon –>Yonhyaku (DONE)
Go –>Gohyaku (DONE)
Roku –>Roppyaku (DONE) [Step 2]
Nana –>Nanahyaku (DONE)
Hachi –>Happyaku (DONE) [Step 2]
Kyuu –>Kyuuhyaku (DONE)
The same warning as the one I gave for the Minute Rule applies here. It’s a functional rule; but historically there may be other reasons for the pattern to be the way we see it.