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Addition and Subtraction
Objectives
To subtract pairs of 2-digit numbers by counting back.
To begin to use empty number line jottings to support calculation.
Resources
Abacus Workbook 3 | Hit the Button (TopMarks) | 📄 0-100 landmarked line | Yellow and red paper or card | Plain (white) paper or card | Scissors
Vocabulary
count | back | subtraction
Today's Lesson
What to Get Ready
Cut up some yellow paper or card to create blank number cards (x8).
Write the following numbers on them: 58, 67, 99, 86, 78, 59, 87, 66.
Do the same with red paper or card (x8), writing the following numbers on them: 22, 23, 24, 32, 33, 34, 42, 43.
For the Extra Challenge, write the following subtractions on white cards:
75 – 22 65 – 21 85 – 34 95 – 42 65 – 41 75 – 34
85 – 22 65 – 23 95 – 34 75 – 42 65 – 33 85 – 41
Introduction
To keep mental recall of times tables facts fresh, ask your student to access Hit the Buttonand select 10x tables, 5x tables and 2x tables.
ACCESS - Hit the Button (TopMarks)
Challenge your student to play each of these times tables twice through, aiming to beat their score on the second go.
Ask:
- How could we work out 65 subtract 24? Do we need to count back in ones?
Encourage thinking and discussion of their ideas for this.
Lead your student to recognising that we can count back 20, and then subtract 4.
Ask:
- What number facts can we use to help?
First find 65 – 20 by counting back in 10s.
Remind them that we know 5 – 4 is 1, so 45 – 4 is 41. So, we still do not need to count back in ones!
Now ask your student to talk with you about how we might work out 85 subtract 24.
Draw on the 📄 0-100 landmarked line, and then also as an empty number line jotting.
Repeat for 85 – 30, 85 – 33, 77 – 33 and 96 – 32.
Ask them to help you to draw the jumps and hops on the landmarked line and to sketch an empty number line jotting alongside.
This video demonstrates how to use the number line to subtract numbers in this way.
Main Activity
Give your student the sets of prepared yellow and red number cards and ask them to lay the cards out face down over the table.
Work in a pair with your student.
One player from the pair chooses a card of each colour and subtracts the number on the red card from the number on the yellow card.
Support your student as they work, encouraging them to try to sketch their own empty number line and to use number facts rather than counting back in 1s.
A correct answer earns a point!
Extra Challenge
Place the prepared subtractions on the table and work with your student to take it in turns to turn over a card.
Each player says if they think the answer will be bigger or smaller than 50 and why.
Win a point for answering correctly any calculations that end in an answer less than 50.
Workbook
To help your student build upon their learning from today, please ask them to complete the activities on page 8 of Abacus Workbook 3.