Which type of number can be written as a fraction?

• A. Rational number
• B. Irrational number
• C. Whole number
• D. Integer

Answer: (A)

A rational number is defined as any number that can be expressed as the quotient or fraction of two integers, where the denominator is not zero. This includes familiar fractions like 1/2 and 3/4, as well as whole numbers (which can be written over 1, such as 5/1) and negative numbers (like -2 can be expressed as -2/1).

Rational numbers are characterized by the ability to be represented in this way, distinguishing them from irrational numbers, which cannot be expressed as a simple fraction. Examples of irrational numbers include π (pi) and the square root of 2, both of which have non-repeating, non-terminating decimal expansions that cannot be expressed as a fraction. Whole numbers are a subset of rational numbers but don't encompass the full range, as they are strictly non-negative integers. Similarly, integers include both positive and negative whole numbers, but they remain a subset of rational numbers too.

Thus, the key attribute of a rational number is its expressibility as a fraction, making it the correct choice in this context.