What is 27% of $80?
- 27% as a decimal is 0.27
- 0.27 × 80 = 21.60
- 27% of $80 = $21.60
Year 9 maths lesson · Percentages
Percentage of an Amount
Calculate a percentage of any amount by converting the percentage to a decimal and multiplying. Includes calculator examples, a down-arrow visual method, and real-world word problems.
- About 5–8 minutes
- 6 quick questions as you go
- Then about 5 minutes of practice
- Have a calculator ready
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Worked examples
What is 35% of $120?
- Percentage → decimal: 35% becomes 0.35
- “Of” → × (times)
- Amount drops down unchanged: 120
- 0.35 × 120 = $42
350 kg of grain loses 4.1% to moisture. How many kg are lost?
- 4.1% as a decimal is 0.041
- 0.041 × 350 = 14.35
- 14.35 kg lost as moisture
What is 73% of $279?
- 73% as a decimal is 0.73
- 0.73 × 279 = $203.67
Before this lesson
It helps to be comfortable with:
- FDP conversions
- Multiplication
Lesson transcript
Everything the lesson says, word for word
Teacher: Hey Jamie, here’s a question for you — what is 73% of $279?
Student: Umm… I know what a percentage is, but I’m not really sure how to find a percentage of a number.
Teacher: That’s OK! We’ll build up to it step by step.
Teacher: Let me ask you something simpler. What’s 1.5 times 8?
Student: 1.5 lots of 8… so that’s 1 lot of 8 plus half a lot of 8… 8 plus 4… that’s 12!
Teacher: Nice! Now what about 0.5 times 8?
Student: That’s half a lot of 8, which is 4.
Teacher: Exactly! Now try 0.25 times 8.
Student: 0.25 lots of 8… that’s a quarter of 8… which is 2.
Teacher: And that’s the same as 25% of 8!
Teacher: See the pattern? To find a percentage of something, you just multiply by the matching decimal!
Teacher: Let’s try 10% of 25. That’s 0.1 times 25 — let’s use the calculator.
Student: 10% of 25 is 2.5!
Teacher: Now a harder one. 27% of $80.
Student: So 27% is 0.27… times 80…
Student: That’s $21.60!
Teacher: Let’s summarise. Take 35% of $120. Change the percentage to a decimal, ‘of’ means times, and drop down the amount. Then pop it in the calculator.
Student: So you change the percentage to a decimal, ‘of’ means times, then drop down the amount and calculate!
Teacher: Last one — a word problem. A coffee roastery receives a shipment of 350 kilograms of green beans. During roasting, 4.1% of the weight is lost as moisture. How many kilograms are lost?
Student: 4.1% as a decimal is 0.041… times 350…
Student: 14.35 kilograms is lost!
Teacher: Now let’s go back to our original question — 73% of $279.
Student: 0.73 times 279…
Student: $203.67!
More Percentages lessons
- Fractions, Decimals and PercentagesConvert fluently between fractions, decimals, and percentages.
- Percentage Increase and DecreaseUse multipliers to increase and decrease amounts by a percentage in one step.
- Reverse PercentagesIf you know a percentage of an amount, work backwards to find the whole.
- Expressing a Quantity as a PercentageExpress a quantity as a fraction, then use the calculator to find the decimal and percentage.
- Percentage Change Year 10Find the percentage change between two values using the multiplier method.
Next lesson: Percentage Increase and Decrease →All Year 9 Number lessonsAll lessons