What are exact numbers and measured numbers?

Exact numbers are values that are counted or defined, such as the number of students in a classroom or defined quantities like 100 centimeters in a meter. They have no uncertainty and are considered infinitely precise. Measured numbers, on the other hand, arise from measurements and include inherent uncertainty due to limitations in the measuring instrument or technique, such as the length of an object measured with a ruler. For example, if a ruler indicates a length of 5.3 cm, that number is a measured number with a degree of uncertainty.