Simone
five-day是用来作定语的，后面可以加名词，意思是“五天的”。
例句：
The workforce have recently been calling for their working hours to be reduced.Many companies have accordingly switched to a five-day week.
工人们最近一直在呼吁缩短工作时间。许多公司于是转成了一周五天工作制。
A five-day working week affords us more leisure time.
每周五天工作制使我们有了更多的休闲时间。
five days可以作状语， 意思是5天。
例句：
They haven't had a square meal for four or five days.
他们已经四五天没吃上一顿像样的饭了。
Soak the walnuts in brine for four or five days.
把核桃放在盐水里泡四五天。
