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# Abaci (or Abacuses) - PowerPoint PPT Presentation

Abaci (or Abacuses). a brief history. Mesopotamian (2700-2300 BC). There is evidence that abaci were used here for addition and subtraction. Mesopotamian (2700-2300 BC). Historic map. Today. Mesopotamian (2700-2300 BC).

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### Abaci (or Abacuses)

a brief history

There is evidence that abaci were used here for addition and subtraction.

Historic map

Today

The abaci were a table of successive columns with each column representing an order of magnitude higher than the next (a bit like our number system). Rather than using decimal (base 10), like we use, they used sexagesimal (base 60).

The number 73 would be written like this:

1 lot of 60 plus 13

Ancient Egyptians used disks of different sizes as counters. It is unclear whether these were used on a frame

Herodotus

5th Century BC

Greek Historian

“The Father of History”

He wrote about the Egyptian abaci and compared them to the Greek abaci. They worked in opposite directions.

They have been using abaci in Greece since 5th century BC.

The oldest abacus discovered so far was Greek and dates back to 300 BC. It is made of slabs of white marble.

The Romans invented a portable abacus for engineers and merchants. It is based on the decimal system.

This is a representation of a Roman abacus.

When you get to 10 move one of these.

When you get to 5 move this one and put the other four beads back.

This column represents millions.

Continue like this until you get to 100 then move one of these.

These two columns are for fractions.

Then move these again to show the numbers from 6 to 9.

Moving the beads in this column represents the numbers 1 to 4.

The Chinese used abaci in the 2nd Century BC. An abacus was known as a suànpán which means ‘counting tray’.

The arrangement is similar to Roman abaci but has extra beads so that both decimal and hexadecimal (base 16) numbers could be used.

Techniques had been developed to use the abaci for addition, subtraction, multiplication, division, square roots and cube roots.

This abacus shows the number 6,302,715,408

The use of abaci spread across the Asia.

In 5th Century AD Indian clerks were using the term shunya (zero) to indicate empty columns on an abacus.

The Japanese started using abaci in 1600 (based on the Chinese one) called a soroban. Even today, pupils in Japanese primary schools are taught to use abaci to aid mental arithmetic.

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