Percentage change, reverse percentages and profit
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 8 practice questions, 1 real past-paper question with the answer explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Was eighty, now sixty-eight
- Percentage change
- A worked example
Read the transcript of the teaching part
Last time
Before we start: last time, in Percentages of quantities, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Was eighty, now sixty-eight
A jacket was eighty dollars and is now sixty-eight. By what percentage was it reduced? And a different jacket is sixty-eight dollars after a fifteen percent sale. What did it cost before? These two questions look similar, but the methods are opposites. Today you learn both, and profit and loss.
Percentage change
The percentage change tells you how big a change is compared with where you started. The formula is: the change, divided by the original, times a hundred. The original is always the starting value, never the new one. This is the number everyone forgets.
A worked example
A price rises from forty dollars to forty-six dollars. First find the change: forty-six minus forty is six. Divide by the original forty: six over forty is zero point one five. Multiply by a hundred: a fifteen percent increase.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Percentage increase and decrease · Percentage increase and.
The whole chapter: Fractions, Decimals and Percentages.
Chapter 3: Fractions, decimals and percentages
- Fractions and mixed numbers 5 min
- Decimals, conversions and recurring decimals 6 min
- Percentages of quantities 5 min
- Percentage change, reverse percentages and profit 6 min
Also for O Level Maths 4024
Which topics come up most in O Level Maths 4024 past papers, counted from every paper since 2004.