Finding a Percentage of a Quantity

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1 Getting Started
2 Watch and Notice
3 Try It Together
4 Work It in Your Copy
5 Class Challenge
6 What Did We Notice?
7 What's Next
Pupil practice

1 - Getting Started ~4 mins

Illustration for Getting Started Picture a shop window with a sign: 25% OFF €60. Roughly how much money would that take off the price? Before we work it out the careful way, what does your gut say, and is there a shortcut hiding in that 25%?

Teacher Notes

Take three hands-up estimates, not open call-outs. Don't confirm or correct yet, just collect a range on the board (some will say €15, some €25, some €6). You are only sparking the question what does 25% of something actually mean? The methods come next.

👇 Mark your steps as done as you complete them.

+5 XP

2 - Watch and Notice ~11 mins

Each bar shows a percentage of an amount built up from equal parts. Look at how each bar is already split into equal parts and work out the amount shown. Notice which parts we use and how we combine them.

Read one part

Teacher Notes

Predict before each reveal.

25% of €60: point at four equal parts, one part is a quarter, €15. Saving €15, pay €45. The fraction shortcut in action.

10% of €80: make-or-break beat. Ten parts, one part is €80 ÷ 10 = €8. Stress dividing by ten is the easiest division, 10% is the key every other percentage builds from.

15% of €40: 10% is €4. Ask how we get the extra 5% before revealing 5% is half of 10%, so €2. Add: €4 + €2 = €6. Bar shows the €4 and €2 segments.

30% of 150: the key one. 10% is 15, three tens give 15 × 3 = 45. They never touch 30 directly. Revoice a strong answer: thirty per cent is just three tens.

75% of €40: introduce three quarters here so it's no surprise later. Each quarter is €40 ÷ 4 = €10, three quarters give 3 × €10 = €30.

👇 Mark your steps as done as you complete them.

+10 XP

3 - Try It Together ~9 mins

Find a percentage by starting from 10%. First find 10% of €35, then build up to 20%. Predict each answer before you check it.

Ten percent, then twenty

Teacher Notes

This round is for talking it through together — pupils take turns at the board and the class agrees or corrects out loud.

Start with 10% of €35 = €3.50 so the class sees a non-round tenth (dividing by ten still works, the decimal point just moves). Then 20% of €35 is two of those, €7 — stack, don't restart. Re-set the bar between the two so pupils see it start fresh. Finally, off the bar and on the board, do 15% of €120: 10% is €12, 5% is half of that (€6), total €18. Watch for the pupil who tries to find 15 lots of 1% — praise it as correct but slower, then show the 10%-plus-5% route is quicker.

+15 XP

4 - Work It in Your Copy ~2 mins

COPYBOOK MOMENT

Before you open your copy, we will do one quick example together on the board so everyone sees how to find 1% by dividing by one hundred, then build a small percentage from it.

Then, in your maths copy, show your 10% (or 1%) step for each problem, then build up to the final answer. Box the answer.

Work these three:

10% of €50, then 30% of €50
1% of €200, then 3% of €200
25% of €48 (spot the fraction shortcut)

Teacher Notes

Board demo first (do not skip): 1% of €400. Divide by one hundred, €400 ÷ 100 = €4. Build 2% as two of those, 2 × €4 = €8. Note the decimal point moves two places left when dividing by 100.

Then pupils work the three copy problems. Walk the room glancing for the 10% or 1% first line, this is whole-class copybook practice, not marking. Look for pupils who jump straight to the answer without showing the building-up step; nudge them to write the 10% or 1% line first. Watch for pupils who divide by 10 instead of 100 when finding 1%.

+10 XP

5 - Class Challenge ~8 mins

Now work each of these in your copy, then we check them together on the board. Each one is a step harder than the last: 20% of €45, then 75% of €60, then 15% of €80, and finally a two-part saving problem, a €240 bike with 35% off. Work out the saving, then say what you would actually pay.

Percentage challenge

Teacher Notes

Pupils work each problem in their copy first, then take turns at the board to show their working while the class confirms before moving on. Keep the board checks brisk rather than over-explaining.

20% of €45 = €9 — two tens stacked (10% is €4.50, doubled).
75% of €60 = €45 — fraction shortcut (three quarters) or three lots of 25%.
15% of €80 = €12 — 10% (€8) plus 5% (€4).
Bike stretch: 35% of €240 is 10%×3 (€72) plus 5% (€12) = €84 saved, so €156 to pay. Watch for pupils who give only the saving and forget the second part (what you pay).

This step runs as a paper/seat task, worked in copies and checked on the board strand by strand — there is no on-screen tool for this step by design.

+15 XP

Pupil practice

Module 3 · Fractions, Decimals and Percentages Number

Lesson 36 · Finding a Percentage of a Quantity

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This lesson is copyright of Coding Ireland 2017 - 2025. Unauthorised use, copying or distribution is not allowed.

Teacher Class Feed

1 - Getting Started ~4 mins

2 - Watch and Notice ~11 mins

Read one part

3 - Try It Together ~9 mins

Ten percent, then twenty

4 - Work It in Your Copy ~2 mins

5 - Class Challenge ~8 mins

Percentage challenge

Unlock the full learning experience

XP