Lesson video

Hi everyone, in this lesson, we're going to learn to calculate percentage change.

Hi everyone, I bought some shoes for 40 pounds and I sold them to my brother for 46 pounds, but don't tell him.

What was the percentage change? I'm going to use a bar model to help me represent how we would calculate percentage change.

Here I have an original amount of 40 pounds and a new amount of 46 pounds.

If I can calculate the difference between those two values, then I can calculate the percentage change.

Here's the formula I would use.

But how does that relate to our question? Percentage change needs at first to find the difference between the new amount and the original amount.

The difference is just six pounds, 46 minus 40.

If I divide that by the original amount and then multiply it by a 100, it will tell me the percentage change.

In this case, it is 15%.

I have increased the value of my shoes by 15%, but don't tell my brother.

I bought a bike for 150 pounds and I sold it to my sister for 225 pounds, but don't tell her.

Which of the calculations would be the correct calculations to find the percentage change? Did you find it? You have to work out the difference between the original amount of 150 pounds and the new amount of 225 pounds.

That's 75, divided by the original amount and then multiply it by a 100.

Let's look at a new question.

I bought a toy for 80 pounds, and I sold it for 52 pounds, find the percentage change.

Let's visualise this question using a bar model.

Here's our formula to calculate percentage change.

We need to find the difference between the original amount of 80 pounds and the new amount of 52 pounds.

So the difference between the original and the new amount was 28 pounds.

If I divide that by the original amount and multiply by a 100, that will calculate the percentage change.

In this case, it is a 35% decrease.

So, the toy that I bought for 80 pounds has decreased in value by 35%.

I bought a bike for 150 pounds, and I sold it for 75 pounds.

which of these calculations would be the correct calculations to work out the percentage change? Did you find it? The original amount was 150 pounds.

The difference between the original amount and the new amount of 75 pounds is 75.

So, 75 over the original amount of 150 times by a 100 would calculate the percentage change.

It would be a percentage decrease though.

Here are some questions for you to try, pause the video and come back when you want to check your answers.

Here's the solutions to question number one.

An item was bought for 12 pounds, that's the original price, sold for 15, so the difference is three, three over 12 gives you one quarter when simplified multiplied by a 100 finds you 25%, yeah.

Let's have a look at some more examples.

Wayne invests 5,200 pounds into a savings account.

His investment matures, so that means he makes some more money.

He's got 5,642 pounds and 45 pence.

Calculate the percentage increase of his investment.

So, let's work out the difference between those two values, the original amount, 5,200 and the new amount of 5,642 pounds and 45 pence.

Let's divide it by the original amount, times it by a 100 and the percentage change would be 8.

5% to one decimal place.

Put it in a calculator and check.

Here's another question.

Joanne bought a netbook for 480 pounds.

A year later she sold it for 360 pounds.

Work out her percentage loss.

So, the percentage change would be the difference between the original amount of 480 pounds subtract the new amount of 360 pounds divided by 480.

and that would find you if you multiply by a 100, a percent change of 25%, it is a decrease.

Here is a question for you to try pause the video and return to check your answers.

Here's the solutions to question number two.

In this question, there's more words and more maths to get through, to find the final answer.

Try and be methodical about how you show your working out.