Which set is closed under subtraction?

Rational numbers are closed under subtraction: subtracting any two rational numbers always gives another rational number. For example, 3/4 − 1/2 = 1/4, which is rational. Whole and natural numbers can give a negative result, and subtracting an irrational number from itself gives 0, which is rational, so the irrational numbers are not closed under subtraction.

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