Decimals and Fractions
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Number line
Number line

Decimals, like fractions, are a way of describing points on the number line that fall in between the whole numbers. If you were using fractions, you'd say that the point halfway between 1 and 2 was 1 1/2. In decimals, you'd call that same point 1.5.

Each digit after the decimal point represents 1/10 of the one before it. So 1.55 means 1 and 1/2 and 5/100. One common use of decimals is in money, where $1.55 means a dollar and 55 cents. Another common use of decimals is in percents, where 50% of 200 means .5 times 200, or 100.

Early measuring systems and mathematics didn't use decimals, because they didn't have a good way to write numbers down. After Indian mathematicians invented the numbers we use today, adding the idea of zero about 500 AD, African mathematicians used them to work more with fractions around 1300 AD. But decimals became really common only with the French Revolution about 1800 AD. French mathematicians encouraged people to use decimals after the Revolution as a new, more scientific, easier to understand way of doing math, that would be more available to ordinary people, so everybody could be an educated citizen.

More about percent
More about fractions

Bibliography and further reading about math:

More Math home

Celebrating Black History Month with the pharaoh Hatshepsut, the queen Shanakdakhete, the poet Phillis Wheatley, the medical consultant Onesimus, the freedom fighters Toussaint L'Ouverture, Denmark Vesey, Yaa Asantewaa, and Samora Moises Machel, and the civil rights leader Martin Luther King, Jr.
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Karen Carr is Associate Professor Emerita, Department of History, Portland State University. She holds a doctorate in Classical Art and Archaeology from the University of Michigan. Follow her on Instagram or Twitter.
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