Lesson video

In this lesson, we're going to be looking at subtracting numbers that are in standard form.

When subtracting numbers in standard form the easiest way to do it is to convert them into ordinary numbers first, then subtract and convert them back into standard form.

So let's start off by converting these two numbers into ordinary numbers.

This would be 50,000 and 30,000.

50,000 subtract 30,000 is 20,000.

We then convert that back into standard form it is two times 10 to the power of four.

Let's look at another example.

Again, we're going to convert these into ordinary numbers before we subtract.

Nine times 10 to the power of negative three is 0.

009, subtracting 0.

0023.

This gets us 0.

0067.

We convert that back into standard form is 6.

7 times 10 to the power of negative three.

You might have noticed, that in both of these examples, we could have just subtracted the two numbers and written times 10th per four for the first example and times 10th to the power of negative three for the second example.

That method only works if the power is in the question are the same.

Hare are some questions for you to try.

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

Here were the answers, for parts e and f you needed to adjust your answer to make sure that it's written in the correct standard form.

With this example, we're going to subtract the numbers again but the powers are different.

So we need to convert both numbers to ordinary numbers before we can subtract.

We can rewrite this example as 300,000 subtract 50,000, which gives us 250,000.

We can then convert that back into standard form.

That gives us 2.

5 times 10 to power of five.

The second example, we're going to do the same thing.

We've got negative powers this time, which means that we're going to be working with decimals.

We can rewrite this calculation as 0.

0038, subtract 0.

00074.

This gives us 0.

00306.

When we convert that back into standard form, it is 3.

06 times 10 to the power of negative three.

Here are some questions for you to try.

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

Here are the answers.

To work out these questions you needed to convert the standard form into ordinary numbers then subtract.

Finally, convert them back into standard form.

Here are some questions for you to try.

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

Here are the answers, 50,000,400 can be partitioned into 50,000,400.

This means that p must be five and q must be four.

In part b, n times 10 to the power of eight is going to be in the hundreds of millions.

This means that 399,600,000 can be rewritten as 400 million subtract 400,000.

So n is equal to four.

In part c, 0.

044 could be rewritten as 0.

5 subtract 0.

006.

This means that a is equal to six and b is equal to five.

Here's a question for you to try.

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

Here is the answer.

To work out the minimum distance from the sun to the earth.

You need to calculate 2.

06 times 10 to the power of eight subtract 5.

46 times 10 to the power of seven.

This gives an answer of 1.

514 multiplied by 10 to the power of eight kilometres.

That's all for this lesson.

Thanks for watching.