What is a decimal?
A decimal is a way of writing numbers using a decimal point to show parts of a whole. For example, 2.5 means two and five tenths, or two and a half.
Our number system is base 10, so each place is worth ten times the place to its right. After the decimal point, the places are tenths, hundredths, thousandths and so on. In 3.47, the 4 means four tenths and the 7 means seven hundredths.
Decimals make it easy to compare and calculate with parts of numbers, which is why money, measurements and scientific data usually use them. Many countries use a comma instead of a point, writing 3,47.
Terminating and repeating decimals
Some decimals end, such as 0.75. Others repeat forever, such as 0.666..., which equals 2/3. Irrational numbers like pi have decimals that go on forever without repeating.
Decimals are especially useful with money. Most currencies divide a main unit into 100 smaller units, such as dollars and cents or euros and cents, so prices are naturally written with two decimal places.
Did You Know?
Decimal fractions were popularized in Europe by Flemish mathematician Simon Stevin in 1585, in a booklet called The Tenth.