Percentages of quantities
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 7 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
- Sale! Thirty-five percent off
- Percent means per hundred
- The multiplier method
Read the transcript of the teaching part
Last time
Before we start: last time, in Decimals, conversions and recurring decimals, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Sale! Thirty-five percent off
Every shop window shows percentages. Thirty-five percent off, twenty percent tax, eight percent interest. A percentage is a fraction out of one hundred. Today you find a percentage of any amount, write one number as a percentage of another, and increase or decrease with a single multiplier.
Percent means per hundred
Thirty-five percent means thirty-five out of a hundred, which is thirty-five hundredths, or zero point three five. Method one is the building blocks. Find ten percent by dividing by ten, and one percent by dividing by a hundred. For thirty-five percent of two hundred and forty: ten percent is twenty-four, so thirty percent is seventy-two, and five percent is twelve. Add: seventy-two plus twelve is eighty-four.
The multiplier method
Method two is faster on a calculator. Change the percentage to a decimal and multiply. Thirty-five percent is zero point three five. Zero point three five times two hundred and forty is eighty-four. Both methods agree, and the multiplier one is the one that works for decimals and awkward 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
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