Three out of four equal parts of something — 3/4, or 75%. Think of a cake cut into four pieces and three of them taken: most of it is gone, but not all. You use it for amounts, for time, and for proportions of people or things: three-quarters of a cup, three-quarters of an hour (45 minutes), three-quarters of the class. The usual pattern is 'three-quarters of' + the thing. It can also stand alone once the thing is understood: 'How much is left?' 'About three-quarters.' The verb agreement follows what comes after 'of', not the word 'three-quarters' itself. Three-quarters of the water is gone — 'water' is uncountable, so 'is'. Three-quarters of the students are here — 'students' is plural, so 'are'. This trips up even confident learners. In everyday speech 'three-quarters of an hour' is very common for 45 minutes, more common than saying 'forty-five minutes' in some contexts, especially about how long something takes. Writing it as a figure — 3/4 — is normal in recipes and notes but not in careful prose.

四分之三、百分之七十五。講時間時特別常用：three-quarters of an hour 就是四十五分鐘，中文會直接說「四十五分鐘」，不會說「四分之三小時」。