Adding and Subtracting Fractions with the Same Bottom Number

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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 Here is a pizza cut into eight equal slices. Two slices are already on your plate, and you reach for three more. Someone worked it out as 2/8 + 3/8 = 5/16 — the tops added AND the bottoms added.

Key point

Have a good look. Is the answer 5/16, or something else? What would you tell them?

Teacher Notes

This is a spot-my-mistake hook. Show the 2/8 + 3/8 = 5/16 attempt and take two or three hands-up answers, not open call-outs. Do not correct yet — the wobble is the point. Listen for a pupil who says the slices are still eighths, they didn't get smaller. Hold that thought for Watch and Notice.

👇 Mark your steps as done as you complete them.

+5 XP

2 - Watch and Notice ~9 mins

The interactive shows four pizzas with like fractions already shaded. Look at the shaded slices on each one, and count them with me.

Teacher Notes

2/8 + 3/8 = 5/8: count the shaded slices together, one to five. Slices never changed size, so the bottom stays 8 — this kills the 5/16 error, the slices did not get smaller.

5/12 - 3/12 = 2/12: started with five twelfths, took three away, pizza shows the 2 left. Count the remaining shaded slices.

7/10 - 4/10 = 3/10: started with seven tenths, took four away, 3 tenths left. Twelfths stayed twelfths, tenths stayed tenths — only the count changes.

4/6 + 2/6: count four, five, six. Pause — ask what happens when the last slice fills? Then reveal 6/6 = one whole. Top matches bottom, every slice full.

👇 Mark your steps as done as you complete them.

+10 XP

3 - Try It Together ~10 mins

Key point

Today we work through these on the pizza together: 3/8 + 2/8, then 6/8 − 1/8, and finally 4/8 + 4/8. Say each answer aloud before we shade it. The last one fills the whole pizza, so watch what the shaded slices tell us.

Slice and total like fractions

Teacher Notes

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

Keep saying the denominator name each time (eighths, eighths) so the bottom number stays fixed in pupils' ears. On 4/8 + 4/8 the count reaches eight eighths — every slice is filled. Ask how many slices are full now? to draw out 8/8 = one whole before the class reads it off.

+15 XP

4 - Work It in Your Copy ~3 mins

COPYBOOK MOMENT

Before you open your copy, watch one worked example on the board so you can see the written layout.

We will write 2/8 + 3/8 with the two fractions one above the other, like this:

2/8
+ 3/8
= 5/8

Add the top numbers only (2 + 3 = 5). The bottom number stays 8 because the slices stay eighths. That is the full method.

Now in your maths copy, work each sum or difference the same way: write the two fractions one above the other and combine the numerators. Remember: the bottom number stays the same. If your answer fills exactly one whole, circle it. You do not need to name it any other way today.

3/8 + 2/8
7/10 − 4/10
4/6 + 2/6

Teacher Notes

Board demo first (do not skip): write 2/8 + 3/8 stacked, tops then bottoms. Say: tops combine (2 + 3 = 5), bottom stays 8. Point to the finished 5/8. One pass only.

Then pupils copy the three list items in the same stacked layout.

Walk the room: bottom number fixed, tops only changing. Watch the slip of adding bottoms (e.g. writing 16). On the last one, circle 6/6 as one whole, no other naming today. Whole-class practice, not marking.

+10 XP

5 - Class Challenge ~7 mins

Today the pizza gives you a target fraction to make each time. Work through them in order: 5/8, then 3/8, then 6/6, then 5/6, then 7/10. Watch for the one that fills every slice on the pizza.

Make the target fraction

Teacher Notes

These are the practice questions — pupils take turns at the board, check each answer, and the class confirms before moving on. Keep the board work brisk rather than over-explaining.

The pizza changes its number of slices to match each target's bottom number. On 6/6 the pizza fills completely — steer pupils to say that is one whole pizza. How many slices are full? is the question that unlocks the one-whole answer.

+15 XP

Pupil practice

Module 3 · Fractions, Decimals and Percentages Number

Lesson 35 · Adding and Subtracting Fractions with the Same Bottom Number

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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 ~9 mins

3 - Try It Together ~10 mins

Slice and total like fractions

4 - Work It in Your Copy ~3 mins

5 - Class Challenge ~7 mins

Make the target fraction

Unlock the full learning experience

XP