Yeah Japanese counting method differs from one in English.
In Japanese, we have a particular names to count numbers in every 4 digit "four zeros" period.
For instance,
Independents: ichi juu hyaku sen [1 10 100 1000]
Mans: 1man 10man 100man 1000man [10000 100000 1000000 10000000]
Okus: 1oku 10oku 100oku 1000oku
[100000000 1000000000 10000000000 100000000000]
However, in English, there are names in every 3 digit "three zeros" period.
Independents: one teen hundred [1 10 100]
Thusands: Thusand TenThusand HundredThusand
[1,000 10,000 100,000]
Millions: OneMillion TenMillion HundredMillon
[1,000,000 10,000,000 100,000,000]
Billions: OneBillion TenBillion HundredBillion
[1,000,000,000 10,000,000,000 100,000,000,000]
Thus,
>how can i say 600 , 800 , 150 million in Japanese ?
refer ⇒ Man: 1man 10man 100man 1000man
[10000 100000 1000000 10000000]
refer ⇒ Oku: 1oku 10oku 100oku 1000oku
[100000000 1000000000 10000000000 100000000000]
600,000,000 roku-oku
800,000,000 hachi-oku
150,000,000 (ichioku+gosenman)= IchiokuGosenman
And
>why we say 376,475 = san juu nana man.. not san juuma "
refer ⇒Man: 1man 10man 100man 1000man
[10000 100000 1000000 10000000]
370000
sanjuu nana man
+
6475
rokusen yonhyaku nanajuu go
=376475 sanjuunanaman rokusen yonhyaku nanajyu go
さんじゅうななまんろくせんよんひゃくななじゅうご
If you still have a question why we say in this way,
just remember this is how we say =)