for or out of every 100, shown by the symbol %
You got 20 percent of the answers right – that means one in every five.
Only 40 percent of people bothered to vote in the election.
an amount of something, often expressed as a number out of 100
What percentage of women return to work after having a baby?
通常在 the／a small／a large…＋percentage of sb or sth 的時候用
E.g. The percentage of unemployed people in this city is relatively small. Nearly everyone works a full-time job.
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
Although she’s recovering from her illness, her rate of progress is quite slow.
I told my assistants to work at their own rate.
The taxi was going at a tremendous rate.
the growth/inflation/mortality/unemployment, etc. rate
The drug has a high success/failure rate.
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
The ratio of men to women at the conference was ten to one/10:1.
The school is trying to improve its student-teacher ratio (= the number of teachers compared with the number of students).
1. the number or amount of a group or part of something when compared to the whole
Children make up a large proportion of the world’s population.
The report shows that poor families spend a larger proportion of their total income on food.
2. the number, amount, or level of one thing when compared to another
The proportion of women to men at my college was about five to one.
The chart shows how weight increases in proportion to height (= the increase in weight depends on the increase in height).
The level of crime in an area is almost always in direct proportion to the number of unemployed.
BBC Podcast: 辨析四個表示“比率” 的近義詞：proportion, rate, ratio, percentage