How to Add and Subtract Decimals for Elementary

How to Add and Subtract Decimals

Adding and subtracting decimals is just like adding whole numbers, but only with a bit of a twist. 😉

Let's Review

When adding 3-digit numbers without decimals, start from the rightmost place value.

Then move from right to left.

Before adding, we make sure that the Ones place digits are lined up properly.

Now, we start adding from the Ones place and move up to the Hundreds place.

There are times when we have to regroup.

Just like when we add this equation.

We regroup when the sum we get is more than 9.

When subtracting 3-digit numbers, we also regroup.

👉 This happens when we subtract a bigger digit from a smaller digit.

So we borrow value from the next higher place.

That's how we got the difference for this equation.

Did you see how we borrowed Tens and Ones from other place values?

Adding Decimals

The way to add decimals is just the same as adding 3-digit numbers. The only difference is the decimal point.

Let's add this equation.

315.25 + 420.71 = ?

The first step is to write this equation in column form .

😃 Make sure that the decimal points are lined up correctly.

Then start adding from the rightmost (👉) place value .

In this equation, we start at the Hundredths place.

Then we move to the left, and add all through the Hundreds place.

✅ The sum of this equation is 735.96 or 735 and 96 Hundredths.

315.25 + 420.71 = 735.96

Great work!

Addition with Regrouping

Can you solve the next addition equation on your own?

475.83 + 957.69 = ?

First, write the equation in column form .

Make sure to line up the decimal points correctly .

Tip: The decimal points must be right over each other, or you'll get the wrong answer! 👍

Add starting from the smallest place value on the right (👉), and add all the way to the leftmost (👉) place value.

🤔 Why do we always start by adding on the right?

👉 When you add, sometimes you need to regroup into a higher place value.

So there's no point adding the bigger numbers first, since more could be added to them from regrouping. 🤓

We see that the sum of the Hundredths digits is 12. It's a 2-digit number...

What should we do? 🤔

Yes, we regroup. That means we carry 1 over to the Tenths column and write 2 in the Hundredths place.

It looks like we need to regroup for all the place values.

So let's do that.

😃 Tip: Remember we're adding decimals, so don't forget to write the decimal point after you get the answer.

We didn't have to regroup the Hundreds place because that's the last digit that we're adding. 😃

✅ The sum for this equation is 1433.52 or 1,433 and 52 Hundredths.

Another Example

Now, let's add this:

15.2 + 4.23 = ?

What did you notice about these numbers? 🤔

The addends don't have the same number of decimal digits.

- The first addend only has 1 decimal digit.

- The second addend has 2 decimal digits.

If we write them in vertical form, we won't have a nicely lined up column on the right and left of the decimal points. 😌

😃 But that's okay because when a number is missing in a place value, we can write a zero in its place to help us keep track of things.

🌟The most important thing is for the decimal points to be lined up !

Now, we can add all the digits starting from the rightmost place value.

✅ The sum that we get is 19.43 or 19 and 43 Hundredths.

15.2 + 4.23 = 19.43

Subtracting Decimals

Do you know how to subtract 3-digit numbers?

Then this will easy for you. 😉

The way to subtract decimals is the same as subtracting 3-digit numbers. The only difference is the decimal point.

Let's try subtracting this equation.

972.846 - 321.603 = ?

The first step is to write the equation in vertical form .

Remember to line up the decimal points carefully.

Now subtract from the rightmost place value first, then move down to the left.

Why do we start at the right? 🤔

When subtracting, we may need to borrow from the next higher place value, so it makes sense to start with the smallest place values.

In this equation, we start at the Thousandths place .

✅ The difference we get is 651.243 or 651 and 243 Thousandths.

972.846 - 321.603 = 651.243

Subtraction with Regrouping

Let's try to subtract another equation.

845.32 - 578.95 = ?

Let's write this in column form first.

🤔 Just by looking we see that most of the digits at the top are smaller than the digits at the bottom.

What does that mean?

Yes! We will need to regroup .

We start from the rightmost place value, and borrow from the next place.

We do the same for all the other place values.

😃 Remember to write the decimal point between the Ones place and the Tenths place.

✅ The difference is 266.37 or 266 and 37 Hundredths.

845.32 - 578.95 = 266.37

Another Example

Now, let's subtract this equation:

13.5 - 1.29 = ?

If we write this equation in column form , with the decimal points lined up.

We see that the number of decimal digits is not the same.

The first number has 1 decimal digit, but the other number has 2 decimal digits.

😃 We can add zeros on the places with no digits to help us keep track of things.

👉 Start subtracting from the rightmost place valu e. In this case, it's the Hundredths place.

0 is at the top and 9 is at the bottom. What does that mean?

Yes, we need to regroup !

✅ The difference is 12.21 or 12 and 21 Hundredths.

13.5 - 1.29 = 12.21

Great work! 🙌

Watch and Learn

Now you can try practice. 😎

How to Add and Subtract Decimals for Elementary

Source: https://www.classace.io/learn/math/3rdgrade/add-and-subtract-decimals

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