Percentages of amounts with and without a calculator, increases and decreases with multipliers, percentage change and simple interest.
What you will learn
- Find a percentage of an amount
- Increase or decrease by a percentage using a multiplier
- Work out a percentage change or profit
- Calculate simple interest
Building blocks, and multipliers
Without a calculator, build from 10% (divide by 10) and 1% (divide by 100).
35% of £240: 10% = £24, so 30% = £72, 5% = £12, 35% = £84.
With a calculator, use a multiplier:
- 17.5% of an amount: × 0.175
- increase by 8%: × 1.08 (100% + 8%)
- decrease by 15%: × 0.85 (100% − 15%)
To write one number as a percentage of another, divide the part by the whole and multiply by 100: 27 out of 60 is 27 ÷ 60 × 100 = 45%.
If 35% of a group are children, the rest, 100% − 35% = 65%, are adults: 65% of 200 = 130 adults.
The rest of this lesson and its 7 practice questions are locked.
In this lesson
- Building blocks, and multipliers
- Percentage change
- Try it: Check a percentage change
7 practice questions, marked as you go; about 25 minutes in all.
Key terms
Original
In this unit: Fractions, decimals and percentages
Calculate with fractions and mixed numbers, move between fractions, decimals and percentages, and solve percentage problems, including reverse percentages.