If '?' represents subtraction, '?' represents addition, '?' represents multiplication, and '?' represents division, what is the result of 15 ? 5 ? 3 ? 2 ? 4?
If '?' means 'greater than', '?' means 'less than', '?' means 'equal to', and '?' means 'not equal to', which of the following is a correct statement? 5 ? 3 ? 5 ? 2 ? 1?