How to Do Subtraction Using the Abacus In Easy Steps
The Usefulness of the Abacus
The abacus is a counting tool which has been put to work by humans over many centuries to perform various arithmetic tasks. By manipulating beads on the abacus with the proper knowledge, almost all math problems can be solved. People can find the answer to multiplication, division, subtraction, and addition problems using the abacus. Today, it is still used by merchants, vendors, and the average person where calculators or pen and paper are not readily available. I have taught techniques for using the counting device to students with vision loss, and I’ve applied the helpful tool in aiding my students with grasping numerical concepts. In addition, I’ve used the abacus for years, receiving my training from masters of the counting tool. Below is a method for working with the abacus to carry out subtraction problems.
Which method do you prefer for solving math problems?
Let's Get Started
- When you look at the abacus, you immediately notice it has rows of four beads beneath a dividing bar. Above the bar, you will see that there are rows of only one bead. To begin, we must make sure the rows of beads are pushed away from the dividing bar as far as they can go. This gives us the value of zero. We say the abacus is “resting at zero.” The picture at the beginning of the article shows an abacus “at rest.
- Next, the abacus works on the base-ten system. This is a system of counting common in most parts of the world. For this reason, from right to left with the rows of beads below the dividing bar, we count: ones, tens, hundreds, thousands, etc.
- For example, if you push the four beads on the first row up to the dividing bar, you have “placed” the number 4 on the abacus. Now, bring the abacus to rest.
- Now, if you push the four beads on the second row up to the bar, you have “placed” 40 on the abacus. It continues on in this manner. Now, bring the abacus to rest.
- In addition, above the dividing bar, the numbers indicate 5 in varying values. For instance, pull down the bead in the first row to the dividing bar. You have placed 5 on the abacus. Now, bring the abacus to rest. Now, pull down the bead above the dividing bar on the second row. You have placed 50 on the abacus. Bring the abacus to rest.
- Finally, if you were to continue doing this, the next bead above the dividing bar on the third row would represent 500, then the next 5,000, and so on. Here is some more information about working with the abacus which is important:
Terms to Know
- Borrow – This process occurs when you subtract a smaller number from a greater one. For example: we borrow 6 from the equation which reads: 10 – 6.
- Pay back – In the above example of 10 – 6, we would have to “pay back” 4 to the abacus. Remember: You always want to keep balance on the abacus; we seek to keep the base-ten counting schemes in mind at all time.
- Place or set – This action occurs when you move beads to the dividing bar to represent a numerical value. Place and set can be used interchangeably.
Now, let’s Work Some Math.
- Our math problem is: 100 - 50.
- Begin by placing 100 on the abacus like shown in the photo.
- Now, we want to take 5 ten’s from 100.
- We know the tens column is showing “0” tens. This means we need to “borrow” 5 ten’s from the 100 column because it is a greater number.
- Because we borrowed 5 tens, we have to “pay back” the abacus 5 tens. (Remember: the abacus works on the principles of the base-ten system.)
- We do this by pulling down the bead representing 50, and “clearing” the bead representing 100 on the third row. This gives us the answer of 50, like shown in the photo. Now, you can bring the abacus to rest.
Let's Do Another Problem
- This time, our subtraction equation is: 100 – 33.
- Begin by placing 100 on the abacus like you did before.
- Now, this time, we want to subtract 3 tens, but there are no tens showing on the device. This means we will have to borrow 30 from 100, or 3 ten’s from 100.
- We know when we borrow 3 tens; we will have to pay back 7 tens. We place 70 on the abacus.
- The number 70 is represented by the 50 bead on the second row with two ten beads beneath it.
- Now, we need to borrow 3 ones from 70 because no ones are showing on the device.
- We push a ten bead back to its starting location, and then we payback 7 ones in the ones column.
- Our answer will read: 67. It should look like the picture.
You have successfully carried out two problems on the abacus in subtraction. You may bring the counting tool to rest. Congratulations!