A rational number is any number that can be written as a fraction where both the top and bottom are whole numbers (and the bottom isn't zero).

Numbers like 1/2, 3/4, and 7/8 are obviously rational numbers because they're already written as fractions. But whole numbers are rational too: 5 is rational because you can write it as 5/1, and even 0 works as 0/1. Negative numbers count as well, so -3 (which is -3/1) is rational.

Here's something surprising: decimals that end, like 0.75, are rational numbers. You can write 0.75 as 75/100, which reduces to 3/4. Even repeating decimals like 0.333... (where the 3s go on forever) are rational. That one equals 1/3.

The opposite of a rational number is an irrational number, which cannot be written as a fraction no matter how hard you try. The most famous irrational number is pi (approximately 3.14159...), which goes on forever without repeating any pattern. The square root of 2 is irrational too.

Mathematicians care about this distinction because rational numbers behave in predictable, organized ways, while irrational numbers don’t fit into a simple fraction. When you're working with measurements, money, or statistics, you're almost always using rational numbers.