Lesson video

Hi everyone, I'm Mr. Lund.

And in this lesson, we're going to be learning about the lowest common multiple and the highest common factors.

Hi everyone.

Multiples are numbers in a times table.

For example the first five multiples of three are three, six, nine, 12, and 15.

What are the first seven multiples of five? There we go.

Are there any common multiples in each list? I've circled the number 15 in the three times table and the number 15 in the five times table.

That number is the lowest common multiple of three and five.

Here are some questions for you to try.

Pause the video and return to check your answers.

Here are the solutions for question number one.

People very often mistake factors and multiples.

Make sure that you can define what each of these term means.

Let's continue our questions.

Pause the video and return to check your answers.

Here are the solutions to question two continued and question three.

Sometimes people mistakenly think that you can find the lowest common multiple of two numbers by multiplying them together.

The example two d shows that that is not the case.

Four times by six is 24, but the lowest common multiple of four and six is 12.

Factors are whole numbers that multiply together to make another number.

For example, to find the factors of 12, think of the numbers that multiply together to make 12.

One times by 12 equals 12.

Two times by six equals 12.

Three times by four equals 12.

Four times by three also equals 12.

As soon as you repeat any, you actually have them all ready.

These are known as factor pairs.

And the factors of 12 are one, two, three, four, six, and 12.

Let's try and find the factors of 20 and 28.

One times 20 equals 20.

Two times 10 equals 20.

Thus three going to 20? No, so let's avoid that.

Four times by five equals 20.

Five times.

Okay, so we repeating ourselves there.

We're not going to use that again.

We have all our factors of 20, one, two, four, five, and 20.

Let's look for the factors of 28 now.

One times by 28, two times by 14, four times by seven, five doesn't go into 28, six doesn't go into 28, seven does, but we've already used seven times by four.

So we have a lot of factors.

The factors of 28 are one, two, four, seven, and 28.

Do we know what the highest common factor of 20 and 28 is from our lists? Do you see? Four is the highest common factor of these two numbers.

Here's some questions for you to try.

Pause the video and return to check your answers.

Here's the solutions to question four and five.

Don't forget when finding factors of numbers, work methodically, try and find factor pairs.

Here's two examples of how you can find factor pairs.

Here's a factor tree and here's my favourite, a factor bug.

Well done for getting this far.

Give yourself a sticker.

Pause the video and return to check your answers.

Oh, here's the final solutions for question six.

You've got to be really organised to work out the highest common factor and the lowest common multiple together.

So take your time with that one.

If you already have, well done for getting that far.