The phrase "a variety of difficult" is not correct in written English.
It is typically used when referring to different types or instances of something that is challenging or hard to deal with, but it needs to be followed by a noun to be grammatically correct.
Example: "The project presented a variety of difficult challenges that the team had to overcome."
Alternatives: "a range of difficult" or "a number of difficult".
Paul Lustig Dunkel and Tania Leon led a variety of difficult pieces throughout the week.
But privately, some said that the move raised a variety of difficult legal and financial questions.
Every postdoc, no matter what field of endeavor, will face a variety of difficult leadership challenges.
If he is confirmed, Mr. Foxx will face a variety of difficult issues.
Under Ms. Leon and Paul Lustig Dunkel on Thursday, its chamber contingent fielded a variety of difficult pieces with grace.
A variety of business sectors have been buffeted by the diffusion of mobile technology, a trend that presents a variety of difficult challenges but interesting opportunities to marketers.
At the center of the tangle is Dr. Stanislaw Burzynski, a Texas doctor and biochemist whose genetically oriented cancer therapy may have cured a variety of difficult-to-treat tumors.
Wire-electro discharge machining (WEDM) is an important non-traditional machining process, widely used for machining a variety of difficult-to-machine materials including titanium alloys with intricate shapes.
State and locally administered quality rating and improvement systems (QRIS) score childcare programs on a variety of difficult-to-observe indicators of quality.
In veterinary medicine, P. aeruginosa is not a widespread pathogen but is responsible for a variety of difficult-to-treat infections.
As a result of the impossibility to purify the poorly soluble PCBA starting material, it is likely that the acid and diol were not present in the required stoichiometric ratio, leading to the formation of a variety of compounds, difficult to separate.
