"formidable questions" is a correct and usable phrase in written English.
It can be used to describe questions which appear to be difficult to answer. For example, "The interviewer posed some formidable questions about my qualifications for the job."
From written essays to the admissions interview, the M.B.A. application process is riddled with formidable questions designed to surface your unique qualities, guiding values, intrinsic motivations and career aspirations.
One of the most formidable questions facing the environmental health research community today is how to translate basic fundamental research into a product (e.g., disease outcome) that meets the needs of its stakeholders--the medical community, regulatory agencies, and ultimately, the citizens of our nation.
Then he read the formidable question his 12-year-old was expected to answer: What is the most pressing problem of our time?
Most embryologists chose instead to focus on understanding how embryos develop a formidable question in itself without thinking much about the evolutionary implications of their work.
This is the formidable question buried under the high-top fades and Cross-Colour jeans of Rick Famiyuwa's natty new film Dope.
In addition, the administrative difficulties of instituting a comprehensive wealth tax are formidable, raising questions about fairness.
The narrator of "Wittgenstein's Mistress," David Markson's fourth novel, is a woman nearing 50 who addresses formidable philosophic questions with tremendous wit and desperation as the last person left on earth.
LT: Piketty's data work is formidable, but questions remain.
The fate of the plane and the people it carried has become a formidable riddle, raising questions about possible terrorism, the identities of passengers and crew members, aviation technology and searching an enormous area that includes both the Indian Ocean and rugged, remote terrain in Asia.
Mayer's task is formidable, and there are questions about how good a leader she really is.
"It is clear that sustainable integration of non-Melanesian refugees in the socioeconomic and cultural life of P.N.G. will raise formidable challenges and protection questions," it said.
