Which number is not a rational number?

A rational number can be written as a ratio of integers; fractions and terminating or repeating decimals are rational. Negative 5 and 4/11 is a fraction-based mixed number, 18.4666… repeating is a repeating decimal, and 7.608 is a terminating decimal. Since 31 is not a perfect square, √31 cannot be written as a ratio of integers, so the number that is not rational is square root of 31.

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