The phrasal adjective cut-and-dried means (1) prepared and arranged in advance, or (2) ordinary; routine. Its exact origins are mysterious, but it seems to date from the early 1700s, when it was used in roughly the same manner as today. Cut-and-dried is often written as either cut-and-dry or cut and dried (without the hyphens)—for example:
A little over a week later, the issue seems a little less cut and dry than the social network had originally painted it. [PC Magazine]
… the facts presented did not lead them to a cut and dried answer for how to dispose of the dog. [South Coast Today]
Neither is a serious error. Cut and dry works because the adjective dry is only slightly different from dried. The second, cut and dried, works because, while the phrase is conventionally hyphenated, cut and dried can function the same as any other two adjectives would. For example, a cut and dried answer is grammatically equivalent to a clear and simple answer, which would not be hyphenated.
In these examples, the writers hyphenate cut-and-dried:
It appears to be a cut-and-dried tale; noble activists and caring government come together to do something positive. [The Daily Star]
When I tell people that I study engineering, they often assume it is a cut-and-dried trajectory … [WSJ]
When the phrase is a predicate adjective, it is almost never hyphenated–for example:
“I thought it was pretty cut and dried,” said Ms. Long, who is a registered nurse. [NYT]
