Lesson video

Hi, I'm Miss Davies.

In this lesson, we're going to be adding and subtracting decimals.

when adding and subtracting decimals, it's just like adding and subtracting integers.

We can work these two questions out in the same way.

Note this, with the right hand question that has the decimal points in it, all of the decimal points are aligned with each other.

When we are adding either decimals or integers, we start from the right hand side.

Seven add five is 12.

We can write this as a two in the ones column and then exchange the one for one ten.

We can do the same with the decimal question.

Seven hundreds add five hundreds is the same as 12 hundreds.

These can be written as two hundreds and one tenth.

Three add one in the left hand question is the same as three tens add to one ten.

Then we need to add the other one ten.

So we have five tens in total.

In the right hand decimal question, we've got three tenths, add one tenth, add one tenth, which is five tenths.

We've now got zero hundreds, add seven hundreds, which is 700.

On the right time question, Zero ones add seven ones, which is seven ones.

Finally, for the integer question, 2000 add 4,000 is 6,000.

And for the decimal, two tens add four tens is six tens.

You can see that our answers have the same digits in the same order.

The right hand question simply have a decimal point in it.

Subtracting decimals is just like subtracting integers.

We look at these two questions, all of the digits are the same.

The right hand question, this has decimal points in it.

Notice that all of these decimal points are in line with each other.

When we are subtracting, whether it is integers or decimals, we start from the right hand column.

In our integer question, this is seven ones subtract four ones, which is three ones.

In our decimal question, We've got seven hundredths subtract four hundredths, which is three hundredths.

Our next column in the integer question is three tens subtract one ten, which is two tens.

In our decimal question, we have three tenths subtract one tenth, which is two tenths.

Our next column in the integer question, we have zero hundreds subtract two hundreds.

In order to complete this, to give a positive result, we need to exchange our two thousands for a one thousand and 10 hundreds.

We now have 10 hundreds subtract two hundreds, which is eight hundreds.

On our decimal question, we're going to do the same.

We're going to exchange 20 for 10 and 10 ones.

The 10 ones subtract two ones is eight ones.

Our final calculation is 1000 subtract 1000, which is zero.

And in our decimal question, it is one ten subtract one ten, which is zero.

You can see that the answers are made from the same digits in the same order.

But our decimal question has a decimal point.

Here's some questions for you to try.

Pause the video to complete your task and resume once you're finished.

Here are the answers.

Make sure that your decimal points are in line vertically, this ensures that all of the place values are in the correct place.

Here's some questions for you to try, pause the video to complete your task and resume once you're finished.

Here are the answers.

Make sure that you've aligned your decimal point vertically.

Also remember to include any exchanges that you have done.

When working with decimals with a different number of decimal places, it is important to line up the decimal point and the place values.

If we are calculating 45.

67 subtract 1.

63, this is not the correct way to set it out.

You can see that our decimal points aren't in line and the place values also aren't in line.

This is the correct way to set this out.

You can see that our three decimal points are all aligned with each other.

The place values are also aligned.

Seven hundredths subtract three hundredths is four hundredths.

Six tenths subtract six tenths is zero tents.

Five ones subtract one one is four ones.

Then we have four tens subtract nothing, which is four tens.

We can check that this answer is correct by doing the inverse.

We can calculate 44.

04 add 1.

63.

If we've done our question correctly, we should get an answer of 45.

67.

Let's start from the right column.

Four hundredths add three hundredths, is seven hundredths.

Zero tenths add six tenths is six tenths.

Four ones add one one is five ones.

Four tens we're not adding anything, so that leaves us with four tens.

This means that our working out is correct.

Here's some questions for you to try, pause the video to complete your task and resume once you're finished.

Here are the answers.

Here is for the difference between the numbers in each column, in the tens column, five subtract seven is not equal to two.

The correct answer is 0.

83.

Here's some questions for you to try, pause the video to complete your task and resume once you're finished.

Here are the answers.

For part A you need add together 1.

69 and 2.

49, this gives an answer $4.

18.

Impart B, you need to add together 1.

39, 2.

49 and 1.

89.

This gives an answer of 5.

77.

That's all for this lesson.

Thanks for watching.