The answer to "Are they the same age?" is not really "I don't know". Try answering "I don't know" to a question during a quiz or an exam, it's very unlikely tha

The answer to "Are they the same age?" is not really "I don't know". Try answering "I don't know" to a question during a quiz or an exam, it's very unlikely that your answer will be considered correct (even if it's actually true that you don't know it). You don't know the answer to the question "Are they the same age" (but it's either true of false), and you don't know the answer to the question "Do car colors differ" (it's either true or false). If you don't know the answer to either question then you don't know whether the answers differ either.