Can someone help me understand this?
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< means 'less than'. 3.5 is less than 4.5, so A is correct. Since -4.5 is NEGATIVE it is less than 0. As for C, since both numbers are negative, it would be the seemingly 'smaller' number that is actually bigger. It may help to think of the numbers on a number line. In the negatives, the numbers start to go in reverse, so the further from 0 a negative number is, the smaller it is. -4.5 IS LESS than -3.5. All answers are correct.
I'm pretty sure that all of them are correct because 4.5 is greater than 3.5, 0 is greater than -4.5, and -3.5 is greater than -4.5.