The letter "x" often represents an unknown number in some Math exercises.

在一些数学练习中，字母“x”通常代表一个未知数。

youdao

A couple of hours after I left the comment, I got a text message from an unknown number.

我评价过后几个小时，收到了一个陌生号码的信息。

youdao

An Infantino spokesman said 10, 000 of the recalled slings had been sold to the UK market, although an unknown number could still be in stores.

Infantino的一位发言人说，从英国市场召回的背巾已有一万条，不过可能还有部分背巾作为库存并未售出，数量尚不明确。

youdao

Diakite,who is also known as Toumba, escaped the attack and is still at large with an unknown number of soldiers from the presidential guard.

VOA: standard.2009.12.07

About 31 Japanese companies had offices in the buildings employing an unknown number of staff.

CNN: Asia pledges cooperation in hunt for attackers

There could be an unknown number of other sports pitches that have been lost, it said.

BBC: Olympics legacy: How can we encourage kids into sport?

That unknown number quite possibly being higher than the jobs created that we can see.

FORBES: If Apple Onshored iPad Production it Would Create 67,000 American Manufacturing Jobs!