Finding the original amount after an increase
Lesson details
Learning outcome
I can calculate the original value, given the final value after a stated percentage increase.
Key learning points
- A bar model can be used to find the original amount after a percentage increase
- A double number line can be used to find the original amount after a percentage increase
- A ratio table can be used to find the original amount after a percentage increase
- In all of these representations a single multiplier can be used to find the original amount after a percentage increase
Keywords
Reciprocal - The reciprocal is the multiplicative inverse of any non-zero number. Any non-zero number multiplied by its reciprocal is equal to 1.
Common misconception
A single digit percentage is incorrectly worked out by dividing by 10 and not 100 e.g 3% = 0.3. This error continues when increasing amounts e.g increase 40 by 3% has a multiplier of 1.3
Remind pupils that to covert a percentage into a decimal we divide by 100. This applies with increase too e.g 120% has a multiplier of 1.2
Teacher tip
After the slides on the traffic lights, use MWBs and change various times for the different parts or get the pupils to choose their own and fill in the other parts based on this. By asking them to choose their own you give them the opportunity consider appropriate values that work with time.
Licence
Lesson video
Loading...
Prior knowledge starter quiz
6 Questions
Q1.A multiplier is the decimal equivalent of a __________.
Q2.Match each question to the correct multiplier.
Q3.Which of the following is the correct calculation for calculating 360 increased by 5%?
Q4.240 increased by 2% is .
Q5.240 decreased by 20% is .
Q6.A box of washing powder contains 20% extra free. The box usually contains 6.5 kg. The special offer box contains kg.
Assessment exit quiz
6 Questions
Q1.‘Of’ can be exchanged for which operation in maths?
Q2.A number is increased by 20%. One part is 20%. What is the total number of parts representing the new number?
Q3.The cost of a TV increases by 15%. The new price is £460. What was the cost of the TV before the price increase? Without calculating the answer, decide whose answers cannot possibly be correct?
Q4.Alex thinks of a number and increases it by 5%. His new number is 252. What was Alex's original number?
Q5.The cost of a TV increases by 15%. The new price is £460. The cost of the TV before the price increase was £ .
Q6.This year the cost of a concert ticket is £94.50. This is an increase of 26% on last year. The cost of the ticket last year was £ .
To help you plan your 8 maths lesson on: Finding the original amount after an increase, download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your 8 maths lesson on: Finding the original amount after an increase, download all teaching resources for free and adapt to suit your pupils' needs.
The starter quiz will activate and check your pupils' prior knowledge, with versions available both with and without answers in PDF format.
We use learning cycles to break down learning into key concepts or ideas linked to the learning outcome. Each learning cycle features explanations with checks for understanding and practice tasks with feedback. All of this is found in our slide decks, ready for you to download and edit. The practice tasks are also available as printable worksheets and some lessons have additional materials with extra material you might need for teaching the lesson.
The assessment exit quiz will test your pupils' understanding of the key learning points.
Our video is a tool for planning, showing how other teachers might teach the lesson, offering helpful tips, modelled explanations and inspiration for your own delivery in the classroom. Plus, you can set it as homework or revision for pupils and keep their learning on track by sharing an online pupil version of this lesson.
Explore more key stage 3 maths lessons from the Understanding multiplicative relationships: percentages and proportionality unit, dive into the full secondary maths curriculum, or learn more about lesson planning.