You can say: One in every four people / one out of five people Two in every five people / two out of five people This is the correct way to express ratios when talking about people. Sometimes, you can see "persons" as the plural form of "person," but that is usually only in very formal context, like legal documents. The most common plural form of "person" is "people."

For 1/4, "one in four people" is one of the correct ways to say it. Or you could say there's a "1 to 3 ratio"

Henryさん、留意点はすべてわかったと思います。特に2/5が確認できてよかった。ありがとう！

四人に一人　One in (every) four personS / people.　'on'　は、間違いです。'every'　は、言っても、言わなくても、どちらでもOKです。 五人に二人　Two in (every) five personS / people. Leeさんが言った通り、日常的にpeopleが普通です。複数の　’ｓ’　を忘れないでね。

For things that cant be divided you use "in". 1 in 4 people have traveled. For things you can divide use a suffix forth, third, sixteenth. example: 1/4 (one forth) of the pizza is going in my belly :)