How to Count to Ninety-Nine on an Abacus With Addition

Tim Truzy is a rehabilitation counselor, educator, and former dispatcher from North Carolina.

History of The Abacus

The exact time at which man began using the abacus is unknown, but today there are various methods for using the abacus to do math. The abacus can be traced back to Africa, Asia, and Eastern Europe. Over almost fifteen hundred years of using the counting tool, techniques for doing addition, subtraction, and complex problem solving has evolved. The design of the abacus has changed, too.

Abaci come in different sizes and shapes. Originally, they were made of pebbles and wood. Later, metal rods were added with beads to slide from side to side to show decimal placement. Some are vertical stand up models. Other abaci are placed on tables and used horizontally.

In all cases, abaci are useful. They still are used by merchants in some countries. They are commonly used in places in the world where calculators are difficult to obtain. Young children around the globe work with the counting tool to help discover fundamentals in math, and visually impaired children learn arithmetic using it too. Here is a basic explanation of how to use the Cranmer abacus (shown in the picture) to count to ninety-nine.

Working with the Cranmer Abacus

1. First, in the picture above, the abacus is “resting at zero.” This means no number has been placed on the device. All the beads are in their starting location. “Resting” means the counting tool is not involved in solving a problem.
2. Next, when you look at the abacus, you will notice a row of beads across the top. These are single beads above the dividing bar. You will also see below the dividing bar, rows of four beads.
3. Finally, moving from right to left, you count and name the columns. A column of beads includes the single bead above the dividing bar and the four beads beneath it. Ones, tens, hundreds, thousands, etc. This abacus will let you work with numbers in the trillions.

Let's Count to Nine

1. We have already identified the first column on the right as the ones. Look at the four beads beneath the bar. Push one bead up to the bar. You have just placed the number 1 on the device.
2. Now, push the other three beads in the row up one at a time, leaving them placed together. You will place: 2, 3, and 4 on the abacus.
3. We want to place the number five on the abacus. Now.

Look again at the beads above the dividing bar. These beads represent different values of five – 5, 50, 500, 5,000 etc. – moving from right to left.

1. Pull the bead representing 5 down to the dividing bar, and leave it there.
2. We realize we have four beads beneath the bar pushed up. We must move these beads back to their starting location to show 5. Leave the bead above the bar pulled down.
3. Now, push the first of the four beads back to the dividing bar. You have just placed 6 on the abacus.
4. Do this with the other three beads left in the column. You will place 7, 8, and 9 on the abacus. It will look like the photo.

Place Ten on the Abacus

To do this, we realize nine plus one equals the desired value. In order to place ten on the abacus, we push up one bead from the second column of four beads beneath the dividing bar. This is the tens column. In the ones column, we return the beads to their starting point or zero. We have just placed ten on the abacus like shown in the picture below.

On to Ninety-Nine

1. We know the bead pushed up on the second column represents 10.
2. Now, if you push up the other three beads in the column one at a time, you will place 20, 30, and 40 on the abacus.
3. To place 50 on the abacus, pull down the bead above the dividing bar and leave it. Return the four beads beneath the bar to their starting point. You have placed 50 on the abacus.
4. Now, push up the first bead again from the column of four under the dividing bar. Leave it placed with the bead representing 50. You have placed 60 on the counting device.
5. Continue on with 70, 80, and 90.
6. Now, add: 90+9. You have placed 99 on the abacus like in the photo. You have done your first math problem on an abacus. Now, you and the abacus can rest.

A Depiction of the Number Ninety-Nine

Tim Truzy (author) from U.S.A. on February 01, 2021:

During this global crisis, I’ve helped people via internet and phone in using the abacus. One thing was apparently clear: Touching and manipulating the beads is very important. Giving children a chance to explore the beads and columns helps them develop their tactile sense and their thinking. I appreciate the visit.

Tim Truzy (author) from U.S.A. on January 02, 2019:

Having extensive experience working with the abacus, one of the most Likeable features of the counting tool is it's durability. Some of the children I've assisted with math have done unspeakable things (intentionally and accidentally) to their abaci. Luckily, the counting tool continued to function properly.

This is why I've written extensively about the abacus, people need durable options for math when those wonderful electronic devices fail to work their magic.