Fractions and decimals expressed as percentages

Before we go any further, we need to know what we mean by ‘percentage’.

In a supermarket, as well as the price of a product being shown, you will often see the cost of a product expressed in a manner which enables you, the shopper, to compare the cost of similar items. For example, the cost of an item may be expressed per 100g or per 100ml.

Example online supermarket with product costing £2.50 for 340g, expressed also as 74p per 100g

Percentages work in the same way. A fraction can be scaled so that the denominator is 100. The numerator then gives the amount out of 100, or “per cent”.

Examples

Using what we have looked at so far, with equivalent fractions and converting fractions and decimals, it’s possible to convert any fraction and any decimal to a percentage.

Three tenths

means the same as . This means that is the equivalent of 30%.

can be expressed as the decimal 0.3. This means that is equivalent to 0.3 which is equivalent to 30%.

Two fifths

is the same as . is the same as , equivalent to 40%.

Similarly, is the same as which is 0.4. Hence , 0.4 and 40% are all equivalent.

Some often used equivalences

Equivalences for one quarter (as 0.25 or 25%), one half (as 0.5 or 50%), three quarters (as 0.75 or 75%), one third (as 0.3 recurring, or 33 and a third %), two thirds (as 0.6 recurring, or 66 and two thirds %)

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Percentages are everywhere. For this week’s context sharing task, find as many examples as you can of percentages being used both within your school or college and outside. Can you find any examples where the percentage is also expressed as a decimal or fraction?

Post in the comments below, including any links you find, or add your images to the Context Sharing Padlet.

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This article is from the free online course:

Maths Subject Knowledge: Fractions, Decimals, and Percentages

National STEM Learning Centre