about ：常可分almost和nearly换用，但about用于表示时间、数量的"大约"时，实际数量可能多也可能少。
approximately ：多用于书面语，指精确度接近某个标准以致误差可忽略不计。
around ：多用于非正式场合，常见于美国英语。
roughly ：指按精略估计，常代替about。
英语四级真题
In the approximately 20 deep-sea crashes over the past 30 years, only one plane's black boxes were never recovered.
出自-2010年6月阅读原文
The American Trucking Association lists approximately 3.5 million professional truck drivers in the U.S.
2018年12月四级真题（第三套）阅读 Section C
英语六级真题
National Institutes of Health (NIH) Biomedical Research Workforce Working Group recommended that the NIH require IDPs for the approximately 32,000 postdoctoral researchers they support.
出自-2013年12月阅读原文
How much would you say is a mid-range bottle of a wine approximately?
2018年6月六级真题(第二套)听力 Section A
Mothers who slept in the same room as their infants, whether in the same bed or just the same room, had poorer sleep than mothers whose babies slept elsewhere in the house: They woke up more frequently, were awake approximately 20 minutes longer per night
2016年6月六级真题（第一套）听力 Section B
Undernourishment during this approximately 1, 000-day window can seriously check the growth and development of children and render them more likely to get sick and die than well-fed children.
2015年12月六级真题（第一套）听力 Section C
柯林斯高阶英汉双解学习词典释义
ADJ-GRADED
大约的；大概的
An approximate number, time, or position is close to the correct number, time, or position, but is not exact.
1. (of quantities) imprecise but fairly close to correct;
"lasted approximately an hour""in just about a minute""he's about 30 years old""I've had about all I can stand""we meet about once a month""some forty people came""weighs around a hundred pounds""roughly $3,000""holds 3 gallons, more or less""20 or so people were at the party"