• (N) Natural Numbers - Natural Numbers are all positive integers from 1 (counting numbers). (1 to infinity)
• (R) Real Numbers - Real Numbers are all non imaginary numbers. (from negative infinity to infinity)
• (Q) Rational Numbers - Rational Numbers are ratios from integers, e.g 1/2, 1 (1/1), 1/4.
• (Z) Integers - Integers are all whole numbers either positive or negative.

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Diagram showing what notations fit within each other.