Seven months have 31 days. How many months have 28 days?

Why this works

This riddle plays on the common assumption that only February has 28 days. While it's true that February typically has 28 days (and 29 in a leap year), every month actually has at least 28 days. So when you consider all the months – January, February, March, and so forth – the answer is that all months have 28 days, making the riddle a clever twist on expectations!