Lesson video

Hi, I'm Mr Chan, and in today's lesson, we're going to learn how to use a decimal multiplier to find the percentage of an amount.

Let us look at an example of using a decimal multiplier to find the percentage in an amount.

So in this example, we're asked to find 32% of £280.

So let's have a look at what we do with this.

32% simply means 32 over 100, because percentages are out of 100.

And in maths the word of, we can think of that as multiplying.

So whenever you see the word of in maths, just think about we can multiply.

280 as such.

So the calculation becomes, 32 over 100 multiplied by 280.

Now, 32 over 100 simply means 32 divided by 100 which is 0.

32, and that's what we call our decimal multiplier when we're finding a percentage of an amount.

The decimal multiplier is 0.

32.

And if we work out what that equals, that will be 89.

6.

Now, we've got to be really careful with this question because it's asking about money.

So we have to convert that back to a monetary amount, which would be £89.

60.

Here are some questions for you to try.

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

Here are the answers.

Let's look at part A as an example.

36% of £240.

So I would have created the fraction 36 over 100 to represent the percentage.

That as a multiplier would be 0.

36.

Working that out on our calculator, we would have got the answer 86.

4, and hopefully you've put it back into the form of money, £86.

40.

Question F, hopefully you got the correct answer with that multiplier, 0.

04, but that will be looked at in the next example.

Here's another example.

In this question we're asked to find 3% of 785.

So again 3%, that would be 3 over 100.

And of, we can multiply, and 785.

So the calculation becomes 3 over 100 multiplied by 785.

Now, with this example you've got to be really careful and figure out 3 over 100 is actually 0.

03.

Don't get confused with that equaling 0.

3, because 0.

3 and 0.

03 are two very different numbers, so with these type of questions where the single digit percentages, just try to be extra careful, 'cause that's a very common mistake.

So in this example, our decimal multiplier is 0.

03.

We can figure out what that calculation equals, that will be an answer of 23.

55.

Here are some questions for you to try.

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

Here are the answers.

Let's look at question two.

A very interesting fact about percentages that you'll notice if you work these out separately, 84% of 50 is actually equal to 50% of 84.

And that happens with all percentages actually.

So that can be explained because multiplication's commutative, that means multiplication works whichever way around you have the numbers, so if you're working out 84% of 50, or 50% of 84, they would actually equal the same thing, and that works with other questions as well.

Here's another question for you to try.

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Here's the answer for question four.

To work out VAT amount, work out the decimal multiplier 20 over 100, you would have got 0.

2 multiplied by £106.

And to work out how much the bike cost including the VAT, you're going to have to add on the £21.

20 to the price of the bike without the value added tax to get a final answer of £127.

20.

Here's another question for you to try.

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Here's the answer for question five.

Mr Hall sells cars and earns 2.

5% commission.

So in this question you've got to be careful about the decimal multiplier you're going to use.

2.

5% your decimal multiplier will be 0.

025.

And if you're unsure about that, remember to put that as a fraction out of 100 to work out the decimal multiplier.

The answer's over there, hopefully you got those correct.

That's all for this lesson.

Thanks for watching.