Valbec - Building Strength with Numeracy. Math Goodies. Math is Fun - Maths Resources. What's In a Number? » Blog Archive » Percentage discounts and bonuses. Introduction By the time people reach the stage of learning about percentages, they are usually very comfortable with the idea that if you add something to something else, and then subtract the same thing, you end up with what you started: a + b – b = a When they apply the same idea to percentages, there is a tendency to do it like this: 100 add 10% = 110 110 subtract 10% = 99 and they then become puzzled at why the two numbers are different. Introducing the Topic Asking the question “What happens if do a 100% increase followed by a 50% decrease?”
Using percentages based on simple fractions can make life easier: If learners pick up on the fact that 33% is not exactly one third, it becomes an opportunity to talk about rounding or about repeating decimals, in this case 33.(3)% and 133.(3) . People may wonder if there is a formula for finding the “inverse” percentage to get back to the original number. R = 100 * d / ( 100 + d ) Back to the Supermarket This difference may be of interest to learners. NRDC : Skillswise - English.
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