Fact: If a and b are non-negative numbers, then ab is non-negative. What is the equivalent contrapositive statement of the above? I think it is: If ab<0, then at least one of a and b <0. Am I right? But this implication doesn't seem quite right to me...shouldn't the correct statement be... If ab<0, then exactly one of a and b <0 ? Could someone please explain? Thank you!