大约

In a sentence

• 我们大约需要两小时完成这个任务。

  We will need approximately two hours to complete this task.

  Here, '大约' indicates an approximation or estimation regarding the amount of time needed.

• 这次演讲听众大约有五百人。

  There are approximately 500 people attending this lecture.

  Here, '大约' is used to give an estimated number related to audience size.

• 大约在两年前，我开始学习中文。

  Approximately two years ago, I started learning Chinese.

  In this usage, '大约' gives an estimated point in time when the action began.