basic mathematics image
 basic mathematics image

Adding decimals

Adding decimals is similar to adding whole numbers.

I strongly recommend though that you review or study the lesson about adding whole numbers before starting this lesson.

Let us start our lesson with something simple.

Look at the following additions:


Note that it is important to align the decimal points and to keep the places in the same column.

This will ensure that you do not add tenths to hundredths or hundredths to thousandths and so forth...

In the first addition problem, we are adding 0.5 to 0.4. It is done in 3 steps!

First, add the tenths (5 and 4) to get 9 tenths

Then, add the ones ( 0 and 0) to get zero.

Finally, write the decimal. It is place immediately after the ones place

Now try to add the followings:


Notice that adding the tenths will give a number higher than 10 tenths

Recall that 1 tenth = 0.1, so 10 tenths = 10 × 0.1 = 1

Therefore, To add these decimals, we must carry over a 1 to the ones place.

The following demonstrates how to add the first two problems:


To add 0.8 to 0.8, we do something similar


Try to do the last problem yourself and you will get 1.6 for an answer.

You could have gotten the answers by adding horizontally.

0.6 + 0.7 = 0.6 + 0.4 + 0.3 = 1 + 0.3 = 1.3 (0.7 = 0.4 + 0.3)

0.8 + 0.8 = 0.8 + 0.2 + 0.6 = 1 + 0.6 = 1.6 (0.8 = 0.2 + 0.6)

0.9 + 0.7 = 0.9 + 0.1 + 0.6 = 1 + 0.6 = 1.6 (0.7 = 0.1 + 0.6)

In practice, when adding vertically,there is no need to write down all those tenths. You can pretend that the decimal point does not exist and try adding decimals as if you were adding whole numbers.

Here is how if we are adding 0.6 to 0.7 and 0.8 to 0.8


Other examples:


Begin by using 0 as placeholders and then add as if you were adding whole numbers.


Now it is time to do a more challenging example. Add the following:


Start by using 0 as placeholders


Then, study and follow the following 5 steps carefully:


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