A common type of question asks children to calculate the price of goods in a sale if everything is reduced by 30%, or how much a special offer box will weigh if it has 25% extra free.

These are the types of problems which children will see in the world around them - when they are shopping with you on a Saturday for example. You can always therefore ask them to calculate the new prices or the new weights.

Nevertheless a common mistake which they would make is that they would only calculate what 30% of the price is. They invariably forget to subtract this 30% from the original price to calculate the sale price.

Similarly they will work out 25% of the weight of the box, but then forget to add this amount back onto the boxes original weight to calculate the new weight.

They should calculate percentage reductions and increases in the following way:

A shop has a sale where everything is 40% off. How much will a £23 pair of jeans now cost?

10% of £23 is £2.30, so 40% is 4 x £2.30, which is £9.20. Now subtract this price from the original cost. £23 - £9.20 = £13.80. The new cost in the sale is £13.80

A box of cereal weighs 750g. A special offer box has 30% extra free. How much does this box weigh?

10% of 750g is 75g, so 30% is 3 x 75g, which is 225g. Now add this amount onto the original weight. 750 + 225 = 975g. The new box weighs 975g

I have provided a worksheet below which can be used to practice these calculations, as well as a blank which can be adapted by yourself if extra examples are required.

Download microsoft_word_percentage_increases_and_decreases.pdf

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