訂正<ていせい>correction usefull→useful 回答<かいとう>answer It is not useful. Rather, we do not have them to make it be useful. We(Japanese) imported kanji<Chinese characters> from China from 5th or 6th century. And we added a Japanese reading (Japanese translation, so-called " kun-yomi ") to most of those. The original Chinese sound (to be precise, Japanized sound) is called " on-yomi ". "yon" and "nana" are kun-yomi and "ichi" "ni" "san" "shi" "go" "roku" "shichi" "hachi" "ku/kyuu" "juu" are on-yomi. The original(traditional) Japanese numerals are "pito（→fito→hito）－tu（→tsu）" "puta（futa）－tu（→tsu）" "mi－tu（→mittsu）" "yo－tu（→yottsu）" "itu（→itsu）－tu（→tsu）" "mu－tu（→muttsu）" "nana－tu（→tsu）" "ya－tu（→yattsu）”"kokono－tu（→tsu）" and "towo（→too）". Nowadays we use on-yomi as numerals basically. But we still use "shi" and "shichi" on idioms like the following. 四面楚歌<しめんそかshimensoka＝be surrounded by enemies >・四、五人<しごにんshigonin＝four or five people>・七転八倒<しちてんばっとうshichitenbattoo＝writhing in agony >・七、八人<しちはちにんshichihachinin＝seven or eight people>・七五三<しちごさんshichigosan＝Japanese festival for children (five-years-old boys and three and seven-year-old girls) > Nowadays we use "yon" and "nana" instead of "shi" and "shichi" basically. The reason is to distinguish similar pronunciations. "ichi" and "shi" and "shichi" are confusing. Nowadays we say usually "ichi-ji<one o'clock>", "yo-ji<four o'clock>" and "shichi-ji<seven o'clock>". But "Nana-ji" is used instead of "shichi-ji" among police officials because the accuracy of time is very important for them. And "futa－yen" and "too－yen" are used instead of "ni－yen二円" and "juu－yen十円" at the stock market because the accuracy of amount of money is very important there.

Nowadays we use on-yomi as numerals basically. But we still use "shi" and "shichi" on idioms like the following. 四面楚歌<しめんそかshimensoka＝be surrounded by enemies >・四、五人<しごにんshigonin＝four or five people>・七転八倒<しちてんばっとうshichitenbattoo＝writhing in agony >・七、八人<しちはちにんshichihachinin＝seven or eight people>・七五三<しちごさんshichigosan＝Japanese festival for children (five-years-old boys and three and seven-year-old girls) >