1. percent (%)百分之(某數字) 一般都是有數字在前面的時候用 (數字＋percent of sb or sth)
for or out of every 100, shown by the symbol %
百分之…（符號為%）
You got 20 percent of the answers right – that means one in every five.
你的答案中20%是對的，也就是說每五個中有一個是對的。
Only 40 percent of people bothered to vote in the election.
只有40%的人肯花時間參加選舉投票。
2. percentage百分率
an amount of something, often expressed as a number out of 100
百分比，百分率
What percentage of women return to work after having a baby?
生完小孩後繼續工作的女性佔多大比例？
通常在 the／a small／a large…＋percentage of sb or sth 的時候用
Percentage被放在 the後時，用單數形動詞：
E.g. The percentage of unemployed people in this city is relatively small. Nearly everyone works a full-time job.
當被放在 a後時，可用動詞單數或複數形式，這由後面所跟的名詞數量而定：
E.g. A large percentage of children in the school come from single-parent families.
E.g. A large percentage of the crop has spoiled.
rate指的是比率，比值，率等，如tax rate稅率,crime rate犯罪率等。
the speed at which something happens or changes, or the amount or number of times it happens or changes in a particular period
率，比率；速率；速度；進度
Although she’s recovering from her illness, her rate of progress is quite slow.
儘管病情正在好轉，但她康復的速度仍很慢。
I told my assistants to work at their own rate.
我告訴我的助手們按照他們自己的進度工作。
The taxi was going at a tremendous rate.
計程車飛速奔馳。
the growth/inflation/mortality/unemployment, etc. rate
增長率／通貨膨脹率／死亡率／失業率等
The drug has a high success/failure rate.
這種藥物治療疾病的成功率／失敗率很高。
ratio 指的是兩個量的比值，其實是強調相比、相除的關係; 比例 (必須有確切的數字)。
the relationship between two groups or amounts that expresses how much bigger one is than the other
比；比例；比率
The ratio of men to women at the conference was ten to one/10:1.
出席會議者的男女比例爲10：1。
The school is trying to improve its student-teacher ratio (= the number of teachers compared with the number of students).
該校正大力優化其師生間的人數比例結構。
proportion有多種用法:
1. the number or amount of a group or part of something when compared to the whole
部分；份額
Children make up a large proportion of the world’s population.
孩童佔世界人口的很大一部分。
The report shows that poor families spend a larger proportion of their total income on food.
報告顯示，貧困家庭食物支出所占其收入比例。
★★★★★★★★★★★★
2. the number, amount, or level of one thing when compared to another
比率，比例
The proportion of women to men at my college was about five to one.
我所在大學的男女比例大約為1：5。
The chart shows how weight increases in proportion to height (= the increase in weight depends on the increase in height).
圖表說明了體重是如何隨著身高成正比上升的。
The level of crime in an area is almost always in direct proportion to the number of unemployed.
一個地區的犯罪率幾乎總是與失業人數成正比。
★★★★★★★★★★★★
BBC Podcast: 辨析四個表示“比率” 的近義詞：proportion, rate, ratio, percentage
https://bbc.in/2ROeuIi
資料來源: https://dictionary.cambridge.org/dictionary/
老師好, 請問若是用 What percentage of …. 來當主詞, 其對應的動詞, 要用單數形? 還是要視 of 後的名詞來看? 謝謝. 例如: What percentage of people in the world have/has mobile devices? What percentage of buildings in California is/are two-story? What percentage of the air is oxygen? 再次謝謝老師!
Nearly 25% of people in the world are…
Why is 25% of people are correct? The subject of this sentence is 25%. Fractions and percentages, like team and staff, can be either singular or plural depending on the object of the preposition following. In this case people is the object of the preposition of. We have already said that people is plural. Therefore, 25% becomes plural in meaning.
Example: Twelve percent of the building has/have been renovated.
The subject is twelve percent, which will be either singular or plural depending on the object of the preposition that follows. In this sentence, the object of the preposition is building, which is always singular. So the correct answer is has.
Source: https://data.grammarbook.com/blog/singular-vs-plural/subject-and-verb-agreement-with-collective-nouns/