过期杂志的英文：
back number

参考例句：

All the out-dated magazines are half-price.
过期杂志一律半价。

back是什么意思：
n. 后面，背面，反面；背，背部；靠背；后卫
v. 支持；后退，倒退；背书；下赌注于
adj. 背部的；后面的；过去的；拖欠的.
adv. 以前；向后地；来回地；上溯

Stand back to back!
背靠背站好！

They are on the back of the menu.
它们在菜单背面。

Our seats on the train were back to back.
我们在火车上的坐位是背靠背的。

It happened far back in the past.
这事发生在久远的过去。

the back of a Chinese robe or jacket
后襟

number是什么意思：
n. 数；号码；算数
v. 给…编号；计算，数

The number was fifty.
该数字为五十。

There is safety in numbers
人多势众

It was an irrational number.
这是一个无理数。

Which number on the card is a prime number?
在卡片上哪一个数字是最初的数字？

The number raised to the logarithm of a designated number in order to produce that designated number.
被升到指定数字的对数上的数量,是为了得到那被指定的数目。