Mildred Taylor, age 16, of Columbus, Ohio, for her question:

WHERE DID THE ABACUS COME FROM?

Abacus is an ancient device used in China and other Asian countries to perform arithmetic problems. It can also be used to add, subtract, multiply, divide and to calculate square roots and cube roots..

In addition to being used at an early date in China and other Asian countries, the abacus was also used by the ancient Greeks and Romans.

The abacus consists of a frame containing columns of beads. The beads, which represent numbers, are strung on wires or narrow wooden rods attached to the frame.

The Chinese abacus is called "suan pan," or "soo poin," names that mean "counting" or "reckoning board." In China, the abacus is used in schools to help students understand the place value in the number system. It has also been adapted to teach blind children arithmetic.

There are several types of abacuses, but they all work on the same principle. A typical Chinese abacus consists of 13 columns of beads. A crossbar separates the beads. Each column has two beads above the crossbar and five beads below it. Each upper bead represents five units and each lower bead equals one unit.

The first column on the right is the ones column. The second column is the tens column. The third column is the hundreds; the fourth column is the thousands; and so on.

The ones column represents numbers from one to nine. Each bead below the crossbar has a value of one and each bead above the crossbar has a value of five ones.

The tens column represents numbers from 10 to 90. Each lower bead in the tens column represents five tens, or 50. The hundreds column represents numbers from 100 to 900. Each bead equals one hundred, or 100, and each upper bead equals five hundreds, or 500.

To place a number on the abacus, move beads to the crossbar. When beads are moved away from the crossbar, they    are cancelled. This means a lower bead is cancelled when it is lowered from the crossbar and an upper bead is cancelled when it is raised from the crossbar.

  Now, let's make an addition calculation on the abacus. To add 2 and 2, first place 2 on the abacus by raising two lower beads in the ones column. Then add the second 2 by raising two more beads in the ones column. The abacus now shows 4, which is the result of adding the 2 and 2.

You can add 2 and 3 in the same way. First place the 2 on the abacus. Then add the 3 by raising three of the lower beads in the ones column. The answer is 5.

But you have used all the lower beads in the ones column. You cannot perform any more calculations until you "clear" the abacus. To do this, cancel the five lower beads and lower one of the upper beads. The abacus still reads 5 because one upper bead in any column on the abacus equals five lower beads in the same column.

More complicated calculations follow this same procedure.