Number facts for kids
- For the book in the Bible, see Numbers (Bible)
A number is a basic idea in mathematics. We use numbers to count things or to measure them. For example, you might count how many friends you have, or measure how tall you are.
Numbers help us understand the world around us. Mathematics uses numbers to explore how things work and to create new inventions. When we use numbers to study the natural world, it's called science. When we use numbers to design and build things, it's called engineering.
There are different ways to think about numbers:
- Cardinal numbers tell us "how many." For example, if you have three apples, the number "3" is a cardinal number.
- Ordinal numbers tell us the order of things. For example, "first," "second," or "third" are ordinal numbers.
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How We Write Numbers
Numbers for People
People use different ways to write down numbers. These systems are called number systems. The most common system we use every day is the base ten number system. It's also known as the decimal number system.
This system is popular because most people have ten fingers and ten toes. It uses ten different symbols, called digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9.
The position of each digit in a number shows its value. For example, the number 23 means (2 times 10) plus 3. The number 101 means (1 times 100) plus (0 times 10) plus (1 times 1).
Numbers for Machines
Another number system is very important for machines, like computers. This is called the binary number system, or the base two system. It uses only two symbols: 0 and 1. These symbols are called bits.
Just like in the decimal system, the position of the bits shows the number's value. For example, the binary number 10 means (1 times 2) plus 0. This is the same as the decimal number 2. The binary number 101 means (1 times 4) plus (0 times 2) plus (1 times 1). This is the same as the decimal number 5.
Names of Numbers
In English, we have special names for some numbers. Especially for numbers that are "powers of ten." These numbers are written with a "1" followed by one or more "0"s.
Here are some examples:
For very large numbers, there are two main ways to name them in English:
- The short scale gives a new name every time a number is a thousand times larger. This is common in most English-speaking countries today.
- The long scale gives a new name every time a number is a million times larger. This scale is less common in English-speaking countries now.
Here are some examples of large numbers:
- 1,000,000,000 – one billion (short scale), one milliard (long scale)
- 1,000,000,000,000 – one trillion (short scale), one billion (long scale)
- 1,000,000,000,000,000 – one quadrillion (short scale), one billiard (long scale)
Different Kinds of Numbers
Natural Numbers
Natural numbers are the numbers we use for simple counting: 1, 2, 3, 4, 5, and so on. Some people also include 0 as a natural number.
These numbers are sometimes called positive numbers. However, not all positive numbers are natural. For example, 1/2 is positive but not a natural number. To avoid confusion, it's often clearer to say "positive integers" or "non-negative integers."
Negative Numbers
Negative numbers are numbers that are less than zero.
Imagine a number line. We mark one spot as zero. Numbers to the right of zero are positive. Numbers to the left of zero are negative. For example, if 1 is one step to the right, then minus 1 (−1) is one step to the left.
