Percentage Increase & Decrease - Using Multipliers | Number | Maths | FuseSchool

In this video we are going to look at how to do percentage increases and decreases, using multipliers. You should already know what percentages are, and how to find them.



Example: A train ticket costing £40 is reduced by 20%. What is the price of the new ticket? 20% of 40 = 20/100 X 40 = £8. £40 - £8 = £32.



We could find a percentage decrease by finding the amount and then subtracting it from the original, like the train ticket example. But there is a much faster way… that is especially great if you have a calculator to hand: using multipliers.



Multipliers are based on decimals, with a slight difference for if you’re doing a percentage increase or a decrease.



For percentage increases, we add the percentage to 100% and then turn it into a decimal. Example: 8% increase = 100% + 8% = 108% as a decimal = 1.08.



The multipliers for percentage increases are always 1 point something if they’re for a 0 to 100% increase.



A 100% increase means double, and will be 2 point something multiplier because 100% + 100% = 200% = 2.0 as a decimal.



But what are multipliers? Why are they 1 point something? We always start with 100% of the item. And then if we want to increase it by 25% we have the starting 100% plus the increased 25%. So that now we have 125%. Which written as a decimal is 1.25. The 1 represents our starting amount and the point 25 represents the percentage increase.



For percentage decreases we subtract the percentage from 100% and then turn it into a decimal. Example: 8% decrease = 100% - 8% = 92% as a decimal = 0.92.



Back to our train ticket example, let’s do it with multipliers this time. A train ticket costing £40 is reduced by 20%. What is the price of the new ticket? It is a percentage decrease, so 100% - 20% = 80% as a decimal = 0.8. £40 X 0.8 = £32

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