Question mark and Unknown quantity

Question mark noun - A punctuation mark (?) placed at the end of a sentence to indicate a question.

Unknown quantity and question mark are semantically related. In some cases you can use "Unknown quantity" instead a noun phrase "Question mark".

Unknown quantity noun - A factor in a given situation whose bearing and importance is not apparent.

Question mark and unknown quantity are semantically related. Sometimes you can use "Question mark" instead a noun phrase "Unknown quantity".