Abacus
An abacus has beads that slide on rods.
It can be used to count, add, subtract, multiply and more.
- the column on the far right is for ones (1,2,3,...)
- the next column is for tens (10,20,30,...)
- the next column is for 100s (100,200,300,...)
- and so on
Just like our decimal number system!
Example: 413
Slide 3 beads UP on the right-most column
1 bead UP on the 2nd-from-right column
4 beads UP on the 3rd-from-right column
The most common abacus is split into a top and bottom section. Each column has:
- Two beads in the top section, and five beads in the bottom one
- Each bead in the top section is worth 5 beads of the bottom section
Have a play with this one (click on the beads or enter a number):
Example:
7 can be made by using one bead on the top row, and 2 beads from the bottom row, because 5 + 2 = 7
Give it a try! See if you can make these numbers on the interactive abacus:
- 9 (Hint: 5 + 4 = 9)
- 23 (Hint: 20 in the tens column, and 3 in the ones column)
- 415
- 1607
The abacus has been around for thousands of years, and is still used in some parts of the world. Sometimes blind people will use an abacus, because they can feel the numbers easily.
Expert abacus users can sometimes do calculations faster than on a calculator, and can even use them to find the square root of whole numbers.