Addition and Subtraction of Decimal Numbers

🏆Practice addition and subtraction of decimal fractions

Simple Operations with Decimal Numbers

We will solve addition and subtraction operations of decimal numbers in vertical form, always keeping in mind the following rules:
• All the rules that are applicable to the addition and subtraction of whole numbers also apply to decimal numbers.
• The decimal points must always be aligned one under the other.
• Numbers must be written in an orderly manner - both to the right of the decimal point and to its left (tenths under tenths, hundredths under hundredths, and so on)

Start practice

Test yourself on addition and subtraction of decimal fractions!

Determine whether the exercise is written correctly in relation to the position of the decimal point:

2.10-3.2

Practice more now

How to Add and Subtract Decimal Numbers

In this article, we will learn how to add and subtract decimal numbers in a simple, easy, and quick way.
In fact, adding and subtracting decimal numbers is very similar to operations with whole and common numbers that we already know and can even solve in our heads without needing to write them down.
Let's remember how to add or subtract whole numbers:
When we have an exercise like 678+879 678+879 
Our intuition naturally prompts us to solve it vertically, so we will write:

A1 - Addition of whole numbers

Excellent! After having remembered how to solve addition and subtraction exercises with whole numbers and having paid attention to critical issues such as:

Writing the numbers clearly by placing the corresponding digits on top of each other (hundreds over hundreds, tens over hundreds, and units over units)
and the correct carry over: noting part of the number above in an orderly manner ("remember that I carry one over..."), let's move on to the addition and subtraction of decimal numbers.

We will always solve the addition and subtraction of decimal numbers vertically!

What we need to pay attention to in the addition and subtraction of decimal numbers:

  • Write the decimal points one under the other.
  • Strictly comply with orderly writing - both in the part of the whole numbers and in the decimals
    Hundreds under the hundreds, tens under the hundreds, units under the units,
    tenths under the tenths, hundredths under the hundredths, and thousandths under the thousandths.
  • Be methodical with the correct carry over - in the same way we do in the addition and subtraction of whole numbers, we will proceed according to the general rules of vertical addition and subtraction.

Suggestion: To make the exercise look more organized we can add the figure 0 0 at the end of the decimal number, to the right, without changing its value.


Now, let's practice

Exercise 1 (addition of decimal numbers)

Solve the exercise: 134.12+56.76=134.12+56.76=

Solution:

Let's write the exercise in vertical form and pay attention to the rules and the important points we have emphasized before.
Notice, the decimal point is under the other decimal point.
In the result, we will also copy the decimal point to the exact place it originally occupied.

A2 - Addition of decimal numbers

Notice that we have correctly carried over when we added 4+6 4+6 and got 10 10 .

A notation like this, for example

A3  - Incorrect notation of addition and subtraction of decimal numbers

Would be a mistake!


Join Over 30,000 Students Excelling in Math!
Endless Practice, Expert Guidance - Elevate Your Math Skills Today
Test your knowledge

Exercise 2 (addition of decimal numbers)

Let's move on to the next exercise:

6.76+12.087=6.76+12.087=

Solution:
Let's write it in vertical form, clearly and correctly:

A4 - Addition of decimal numbers

Note: It is extremely important to write in an orderly and clear manner, both the side of the whole numbers and the decimals, to obtain a correct result.
If you do not see the exercise in a very orderly way you can add a 0 that will not affect the numerical value (marked in pink), and thus, get a clearer view of the exercise.


Exercise 3 (addition of decimal numbers)

Now we will see an exercise with carrying over to the part after the decimal point:
Solve the exercise
185.28+76.9= 185.28+76.9= 

Solution:
Let's write it correctly:

A5 - Addition of decimal numbers with carrying over to the other side of the decimal point

We can see that the number we carried over passed to the other side of the decimal point, this is totally correct.


Do you know what the answer is?

Now let's move on to a subtraction exercise.

Exercise 1 (Subtraction of Decimal Numbers)

2.31.8=2.3-1.8=

Solution:
Let's write it in an organized way:

A7 - Subtraction of decimal numbers with borrowing that goes to the other side of the decimal point

Notice that we need to borrow, we will do it according to the same rules of adding and subtracting whole numbers.


Exercise 2 (Subtraction of Decimal Numbers)

Example of an advanced exercise: 
3.031.69=3.03-1.69=

Solution:
In this exercise, we will need to borrow twice.

A9 - Subtraction of decimal numbers with borrowing that crosses the decimal point

Infallible recommendation:
To always know how to write the exercises correctly, it is advisable that, after noting the first decimal number, you place the decimal point of the second fraction directly below the decimal point of the first fraction, and only after doing this, write the remaining numbers.


Check your understanding

When can sums and subtractions of decimal numbers be solved without using the vertical form?

In general, we recommend solving additions and subtractions of decimal numbers only in vertical form.
In case the exercises are very simple (without carrying and without too many digits) they can be solved without arranging them in vertical form. Clearly, everything depends on the instructions noted in the exam.
Example of solution: 3.32+1.12=3.32+1.12=
Let's add the units and we will get 55
Let's add the tenths and we will get 44
Let's add the hundredths and we will get 44
The solution is 5.445.44


Examples and exercises with solutions for addition and subtraction of decimal numbers

Exercise #1

Determine whether the exercise is written correctly in relation to the position of the decimal point:

2.10-3.2

Video Solution

Step-by-Step Solution

The problem requires us to verify if the subtraction exercise of the decimal numbers is written correctly, focusing on the position of the decimal points.

Step-by-step:

  • Step 1: Identify the given numbers, 2.102.10 and 3.23.2.

  • Step 2: Align these numbers by their decimal points for proper subtraction.

Upon alignment, the numbers are:

2.102.10
3.2-3.2.

To correctly align them for subtraction, we can rewrite 3.23.2 as 3.203.20 to match the number of decimal places:

2.102.10

3.20-3.20

The decimal points are aligned correctly in both numbers, confirming that the exercise is set up accurately regarding the position of the decimal point.

Thus, the answer to the problem is Yes.

Answer

Yes.

Exercise #2

Determine whether the exercise is correctly written or not.

The position of the decimal point corresponds.

38.15-122.3

Video Solution

Step-by-Step Solution

To determine whether the exercise is set correctly, we need to align the decimal points of the two numbers involved in the subtraction operation:

1. The given numbers are 38.15 and 122.3.
2. We write them down vertically, aligning by the decimal points:

038.150122.3 \begin{array}{c} \hphantom{0}38.15 \\ - \hphantom{0}122.3 \\ \end{array}

3. Notice that the number 38.15 has two decimal places (hundredths), while 122.3 only has one decimal place (tenths). Therefore, the hundredths place in 122.3 is effectively considered as "0" to match the decimal places of the first number. Upon aligning the decimal points, 38.15 and 122.3 indeed match as:

038.15122.30 \begin{array}{c} \hphantom{0}38.15 \\ - 122.30 \\ \end{array}

4. This check confirms that there is an incorrect statement regarding "The position of the decimal point corresponds," as the numbers are aligned at the decimal points considering all decimal places are consistently represented.

Therefore, the statement "The position of the decimal point corresponds" is Not true.

Answer

Not true

Exercise #3

Determine whether the exercise is correctly written or not.
The position of the decimal point corresponds.

38.15-122.3

Video Solution

Step-by-Step Solution

To solve this problem, we'll follow these steps:

  • Ensure the decimal numbers are aligned correctly according to their decimal points.

  • Perform the arithmetic operation to verify logical correctness.

Let's analyze the given numbers:

  • The first number is 38.1538.15.

  • The second number is 122.3122.3. We can express this as 122.30122.30 to simplify alignment.

Align the numbers vertically based on their decimal points:

38.15 \quad 38.15
122.30 -122.30

Notice the decimal points are aligned. Now, perform the subtraction:

Start from the rightmost column:

  • (50=5) (5 - 0 = 5)

  • (13=Borrow 10, becomes 113=8) (1 - 3 = \text{Borrow } 10, \text{ becomes } 11 - 3 = 8)

Move to the next left column (tens column):

  • (borrowed 18 becomes 7) (\text{borrowed } 1 \rightarrow 8 \text{ becomes } 7)

  • (72=5) (7 - 2 = 5)

  • (32=1) (3 - 2 = 1)

  • (The result is negative because 38.15 is less than 122.30) (\text{The result is negative because 38.15 is less than 122.30})

Result of the subtraction is 84.15 -84.15 .

Since the exercise primarily asks if the decimal points are aligned correctly, and they indeed align correctly, we conclude:

The exercise is written correctly with respect to decimal alignment.

Therefore, the solution to the problem is True.

Answer

True

Exercise #4

Determine whether the exercise is correctly written or not.

The position of the decimal point corresponds.

99.38-99.38

Video Solution

Step-by-Step Solution

To effectively assess the problem, we should confirm if the decimal points in the subtraction of two identical numbers, 99.3899.3899.38 - 99.38, are aligned correctly.

Step 1: The numbers involved in the subtraction are 99.3899.38 and 99.3899.38, both having the same number of digits before and after the decimal point.

Step 2: Check the alignment of the decimal points in the subtraction setup. In properly written subtraction involving decimals, the decimal points must align vertically to ensure correct digit placement.

Step 3: The setup displays the numbers:

  • 99.3899.38
  • 99.3899.38

Each digit before and after the decimal is in perfect vertical alignment, confirming correct decimal point alignment.

Conclusion: The exercise is correctly written in terms of decimal alignment.

The correct answer to the problem is True.

Answer

True

Exercise #5

Determine whether the exercise is correctly written or not.

The position of the decimal point corresponds.

88.100-88.101

Video Solution

Step-by-Step Solution

To determine if the exercise is correctly written, let's ensure the decimal points are aligned properly in the subtraction problem. We have:

  • Top number: 88.10088.100
  • Bottom number: 88.10188.101

We verify that each digit is aligned according to its place value:

  • The units column aligns (88 above 88).
  • The tenths, hundredths, and thousandths columns align (00 above 11).
  • The decimal points are directly above one another.

Since the digits and decimal points are aligned properly according to the rules of subtracting decimal numbers, we can conclude that the setup of the exercise is correct. Therefore, the assertion that "the position of the decimal point corresponds" is True.

In conclusion, the exercise is correctly written regarding the alignment of the decimal point.

Answer

True

Do you think you will be able to solve it?
Start practice