Percentages – Year 9 maths lesson
Lesson 36 of 38 in the Year 9 maths course
UK version. UK school years, UK spelling and pounds (£). · US Math Department
A complete 45-minute lesson for Year 9 (ages 13–14) that runs on this page – at school or at home. Every answer is marked straight away, with a worked explanation.
- Time
- 45 minutes + 20 min homework
- Year
- Year 9 (ages 13–14)
- You need
- Paper, a pencil and this page
- Marked
- Instantly, with explanations
For parents: how to use this lesson
You don't need to know this topic yourself. The lesson explains each step on screen, one tidy step at a time. Every answer is marked straight away with a worked explanation, so you never have to mark anything.
- Read what your child will learn and the big ideas together.
- Press Start the lesson below and sit with your child for the teaching and the worked examples (about 19 minutes).
- Let them do the practice on their own. They choose Getting started, On track or Challenge – start on On track and move up after a few right in a row.
- Finish with the exit ticket and the talk question: “Why does a 50% rise followed by a 50% fall not bring you back to the start?”
- Later that day or the next day: the homework (20 minutes), then a practice test.
Watch out for
- Finding the percentage and forgetting to add or subtract it. Use a multiplier: 1.2 already includes the original.
- Taking 20% off a sale price to find the original. Divide by 0.8 instead.
Tip for home: Work out sale prices and tips together.
What your child will learn
We are learning to find percentages of amounts, percentage increases and decreases, and reverse percentages.
Success looks like
- I can find a percentage of an amount.
- I can increase and decrease by a percentage.
- I can find a percentage change and an original amount.
Key words
- multiplier
- the decimal you multiply by
- increase
- make bigger
- decrease
- make smaller
- original
- the amount before the change
What to have ready
- Paper and a pencil
- This page on a computer, tablet or phone
- For the hands-on part: Compare real sale prices: is "30% off" better than "buy 2 get 1 free"?
The big ideas (for the adult)
To find a percentage of an amount, find 10% or 1% first, or use a multiplier: 15% of 80 = 0.15 × 80 = 12.
For an increase of 20%, multiply by 1.2; for a decrease of 20%, multiply by 0.8.
Percentage change = change ÷ original × 100. To find an original amount, divide by the multiplier.
The lesson, step by step
| Part | Time | How it is checked |
|---|---|---|
| Starter: quick recall | 5 min | Marked by Classfern |
| Teaching input | 10 min | Not assessed, self-checked |
| Worked examples and guided practice | 9 min | Not assessed, marked by Classfern |
| Independent practice | 15 min | Marked by Classfern |
| Plenary and exit ticket | 6 min | Marked by Classfern, self-checked |
Starter, "your turn", practice and exit ticket are marked by Classfern. Worked examples and teaching are not assessed. The hands-on task and the reflection are self-assessed. Explanations in talk are judged by the parent and not recorded.
The lesson
It runs here on the page. No sign-up and no names – progress is kept only in this browser.
Homework and practice at home
20 minutes: 10 practice questions, 3 multiple-choice questions and 2 to remember from earlier work, then a short reflection. New questions every time, all marked instantly.
More practice
More Year 9 maths lessons
- Prime factors, HCF and LCM
- Rounding and estimation
- Bounds and error intervals
- Standard form
- Laws of indices
- Powers and roots
- Units and measures
- Area of triangles, parallelograms and trapeziums
- Circles: circumference, area, arcs and sectors
- Volume and surface area
- Angle facts and parallel lines
- Angles in polygons
- Pythagoras' theorem
- Trigonometry: SOH CAH TOA
- Transformations
- Similarity and congruence
- Quadrilaterals and symmetry
- Coordinate geometry
- 3-D shapes, plans and elevations
- Quartiles, box plots and spread
- Pie charts and time series graphs
- Sampling
- Relative frequency and expected outcomes
- Venn diagrams and conditional probability
- Algebraic notation
- Substitution
- Simplifying expressions
- Expanding brackets
- Solving linear equations
- Inequalities
- Rearranging formulae
- Sequences and the nth term
- Straight-line graphs
- Graphs of functions
- Ratio
- Speed, density and pressure
- Scale drawings and maps
Curriculum
National Curriculum for England, Year 9: “solve problems involving percentage change, including: percentage increase, decrease and original value problems and simple interest in financial mathematics”
GCSE subject content R9: “define percentage as ‘number of parts per hundred’; interpret percentages and percentage changes as a fraction or a decimal, and interpret these multiplicatively; express one quantity as a percentage of another; compare two quantities using percentages; work with percentages greater than 100%; solve problems involving percentage change, including percentage increase/decrease and original value problems, and simple interest including in financial mathematics”
Contains public sector information licensed under the Open Government Licence v3.0.
Our lessons and questions are our own. They are not written or endorsed by any government department, testing agency or exam board.