Calculate a Percentage Increase

This activity is about calculating a percentage increase.

We are using a calculator for this activity!

 

We can see percentage increases everywhere.

A common place to see it is in the supermarket when we are sometimes given an extra % free.

 

 

We can calculate simple percentage increases easily without a calculator.

For example, the box above usually has 200 g of cereal in it, but they are giving away an extra 30%.

 

We can work out 30% of 200 and add it to the 200 g already in the box.

So, 10% of 200 = 20 g

30% = 3 x 10% = 3 x 20 = 60 g

New weight with extra free = 200 g + 60 g = 260 g

 

When they get a little more tricky, like a 59.5% increase, it is easier and quicker to use a multiplier and a calculator!

Recap - the multiplier is basically, the decimal!

 

 

Example

Increase 82 ml by 18%.

 

Answer

To find 18% it is 18/100 = 18 ÷ 100 =  0.18 as a decimal.

To increase 82 ml we want the 82 ml + 18%.

So, we could do the whole thing in one move if we multiply by 1 to get the 82 and 0.18 to get the 18% increase. So, we multiply by 1.18.

 

Therefore, £82 x 1.18  = £96.76

 

Remember, when working with money, we need to round to two decimal places.

 

Let's try some questions now.