When the answer is
x must be at least less than 0.5 (i.e., x<0.5).
where 0.5 is the specific answer I am looking for, what is the proper question?
x must be at least less than what value?
does not sound like a proper sentence. "What is the maximum possible value for x?" does not work because x cannot be 0.5.
I also feel "at least" is used improperly here but "x must be less than what value?" cannot work (whether grammatically or otherwise) because for this question 0.4 is a correct answer, but I want it to be wrong.