It's a bit inconsiderate of her not to let you know when she expects to arrive.

她不让你知道她什么时候会到，这样做有些不体谅人。

《柯林斯英汉双解大词典》

The microwave beeps to let you know when it has finished.

微波炉烹饪完毕时会发出哔哔声提醒你。

《牛津词典》

A meeting will be held at lunchtime, Tuesday October 9th, the day before the course begins, on the school tennis courts to let you know the lesson time.

10月9日（星期二），也就是课程开始的前一天，学校将在午餐时间于网球场召开会议，告知大家课程时间。

youdao

In a poker game you do not want to let your opponents know if your cards are good or bad.

VOA: special.2009.11.22

So, many of you are new to the Boston area, now I still realize, and I want to let you know it's not required that you be a Red Sox fan to be at MIT.

你们中很多人新来到波士顿地区，现在我仍认识到，我想让你们知道在麻省理工学院,不一定必须做一个红袜队的球迷。

麻省理工公开课 - 化学原理课程节选

Just want to let you know that there will be an information session this afternoon, from 3 to 4:30 in Harvard Hall, room 103.

希望大家知道,今天下午有一个咨询会，在哈佛大厅103教室，从三点到四点半。

哈佛公开课 - 幸福课课程节选

Often I thought of trying to let you know what I knew I would do.

NEWYORKER: History of a Disturbance

As always, we will continue to let you know first about developments at the distillery.

FORBES: Maker's Mark Sincerely Apologizes For Almost Diluting Its Bourbon

And his mother just wanted to let you know that he is special needs.

WHITEHOUSE: The White House