# Cardinal numbers

Cardinal numbers (also called whole numbers, natural numbers, or counting numbers) are those used to count physical objects in the real world, such as

0, 1, 2, 3, 4 .....
They are integers that can be zero or positive. They assume that the things being counted are not divisible. So we can have 4 cars, but never 3½ cars.

Formally, counting numbers are the set of all non-negative integers.

Cardinal numbers are also called counting numbers.

## Statistics can confuse you

You may have heard something like "the average household has 1.8 children". Obviously, every family has a whole number of children. The average is found by adding up all the children and dividing by the number of households. Once you do that division you no longer have a cardinal number. That result is a statistic and is actually a real number - one that can have fractional parts.

## Cardinality

When we have a set of objects, the cardinality of that set is the number of objects it contains. See Cardinality.