Problematic Natures and Philosophical Questions Aristotle means one-to-one correspondence between 'problems' and propositions. He is defining a technical meaning of 'problem' to refer to yes / no questions.
"The difference between a problem and a proposition is a difference in the turn of the phrase.
For if it be put in this way, "'An animal that walks on two feet" is the definition of man, is it not?' or '"Animal" is the genus of man, is it not?' the result is a proposition: but if thus, 'Is "an animal that walks on two feet" a definition of man or no?' [or 'Is "animal" his genus or no?'] the result is a problem. Similarly too in other cases. Naturally, then, problems and propositions are equal in number: for out of every proposition you will make a problem if you change the turn of the phrase."
The context is Aristotle's aim to "find a line of inquiry whereby we shall be able to reason from opinions that are generally accepted about every problem propounded to us, and also shall ourselves, when standing up to an argument, avoid saying anything that will obstruct us."
He is trying to pin down the essence of logic as it applies to arguments about any subject at all, in order to avoid poor reasoning.
Aristotle does not think that the only problems we ever consider are yes / no questions. If that was what he thought, let's stop reading him now because that would be too dumb. And Aristotle may have been many things, but dumb was not one of them.