Final answer:
All given options - 81, 90, 125, and 200 - result in rational answers because they are whole numbers and can be expressed as fractions with the denominator of 1.
Step-by-step explanation:
The question asks which numerical expression results in a rational answer. Rational numbers are numbers that can be expressed as a fraction where both the numerator and the denominator are whole numbers, and the denominator is not zero. The options provided are single whole numbers: 81, 90, 125, and 200. All these numbers can be expressed as fractions with the denominator of 1 (for example, 81 can be written as 81/1, 90 as 90/1, and so forth). Therefore, each option results in a rational answer because they are all whole numbers and can be expressed as a fraction with an integer in the numerator and 1 in the denominator.