Number line

Adding numbers is like walking along a path, the number line. To add two small numbers, like 7 + 4, you can just start from the 7 and walk forward 4 spaces, and then see where you are on the number line, and there you are at 11. If you want to add a negative number, like -3, we call that subtraction.

What if you want to add two bigger numbers, like 343 + 546? Suppose you had two big flocks of sheep, and you wanted to know how many sheep you had altogether? It would take too long to count so many sheep, and you might lose count somewhere along the way. For many thousands of years people tried to figure out easier ways of doing this, and finally, about 500 BC, people in the Persian Empire (or possibly China) invented the abacus.

But what if you don't have an abacus handy? It took another six or seven hundred years for mathematicians to work it out, but finally mathematicians in India invented placenumbers about 500 AD.

Professor Carr

Karen Eva Carr, PhD.
Assoc. Professor Emerita, History
Portland State University

Professor Carr holds a B.A. with high honors from Cornell University in classics and archaeology, and her M.A. and PhD. from the University of Michigan in Classical Art and Archaeology. She has excavated in Scotland, Cyprus, Greece, Israel, and Tunisia, and she has been teaching history to university students for a very long time.

Professor Carr's PSU page

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