Why the mixture of *on* and *kun* readings of numbers?


One thing that always puzzled me was why some terms and names that are based
on numbers will mix the _on_ and _kun_ readings. I never really understood the
rules for that, but it occurs to me that there must be some.

For example, the word _yakuza_ is derived from 8-9-3, a no-score hand in the
花札 ( _hanafuda_ ) card game. This comprises:

> や — 8, _ya(ttsu)_ , a _kun_ reading  
>  く — 9, _ku_ , an _on_ reading  
>  ざ — 3, _za_ (for _san_ ), an _on_ reading

Similarly, the famous Admiral Yamamoto had a given name of Isoroku (meaning,
curiously, "56"), which mixed _kun_ readings (or their variants) for 5 and 10
plus the _on_ reading for 6.

I just want to know how to make sense of this — or if it is even necessary
that it make sense. Perhaps it is simply a matter of putting together sounds
that the originator(s) of the term found pleasing?

**Edit** : I want to add that the usages sometimes seem capricious to me, as
when you hear 二人（ふたり）to refer to two people but 二人前（ににんまえ）to refer to a
restaurant serving for two people or the task that two people have before
them, although you can hear ふたりまえ there as well.




This is actually an interesting topic, here's a quote from
[wikipedia](http://en.wikipedia.org/wiki/Hybrid_word#Japanese):

> In Japanese, hybrid words are common in kango – words formed from kanji
> characters – where some of the characters may be pronounced using Chinese
> pronunciations (on'yomi, from Chinese morphemes), and others in the same
> word are pronounced using Japanese pronunciations (kun'yomi, from Japanese
> morphemes). These are known as jūbako (重箱) or yutō (湯桶) words, which are
> themselves examples of this kind of compound (they are autological words):
> the first character of jūbako is read using on'yomi, the second kun'yomi,
> while it is the other way around with yutō. Other examples include 場所 basho
> "place" (kun-on), 金色 kin'iro "golden" (on-kun) and 合気道 aikidō "the martial
> art Aikido" (kun-on-on).

For more in-depth reading into the topic, see
[here](http://en.wikipedia.org/wiki/Sino-Japanese_vocabulary).




This is actually an interesting topic, here's a quote from
[wikipedia](http://en.wikipedia.org/wiki/Hybrid_word#Japanese):

> In Japanese, hybrid words are common in kango – words formed from kanji
> characters – where some of the characters may be pronounced using Chinese
> pronunciations (on'yomi, from Chinese morphemes), and others in the same
> word are pronounced using Japanese pronunciations (kun'yomi, from Japanese
> morphemes). These are known as jūbako (重箱) or yutō (湯桶) words, which are
> themselves examples of this kind of compound (they are autological words):
> the first character of jūbako is read using on'yomi, the second kun'yomi,
> while it is the other way around with yutō. Other examples include 場所 basho
> "place" (kun-on), 金色 kin'iro "golden" (on-kun) and 合気道 aikidō "the martial
> art Aikido" (kun-on-on).

For more in-depth reading into the topic, see
[here](http://en.wikipedia.org/wiki/Sino-Japanese_vocabulary).

