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Addition and Subtraction
Objectives
To add a single-digit number to a 2-digit number, bridging 10.
Resources
Abacus Workbook 1 | Red pen | Blank cards or paper | 📄 100 square | 📄 0-100 beaded line
Vocabulary
add | bridge 10 | multiple of 10
Today's Lesson
What to Get Ready
Write the following calculations on separate blank cards / pieces of paper:
22 + 5, 27 + 5, 38 + 4, 33 + 4, 76 + 5, 43 + 5, 35 + 7, 23 + 6
Introduction
Before you start the lesson, watch this Recap Video with your student.
Show your student the 📄 100 square. Ask your student if they can find the multiples of 10 (10,20,30…) and colour th
em in red.
Now, also colour the multiples of 10 in red on a 📄 0-100 beaded line.
Say: ‘These are special numbers – they match the ends of groups of 10 beads on the 100 bead string and are called multiples of 10.’
Next, write 37 + 6.
Say: ‘What will happen when we add 6 to 37? We will cross a red number (40).’
Add 3 (to reach 40) and then 3 more (to reach 43) on the grid.
Write 37 + 6 = 43.
Repeat, showing how we cross a ‘red’ number- a multiple of 10 - when adding 8 to 45.
Main Activity
Now, look at the cards with the calculations written on. Discuss which calculations will cross a multiple of 10 (a red number).
Can your student sort them into 2 piles?
Pile 1: calculations that will cross a multiple of 10
Pile 2: calculations that will not cross a multiple of 10.
Next, ask your student to take a card from Pile 1 in turn and point to the multiple of 10 it will cross on the 📄 0-100 beaded line.
To check their predictions, they should then add the 2 numbers, using the ‘T10’ recording strategy from Step 15 Lesson 1 to record how the 1-digit number is split.
Workbook
To help your student recap upon previous learning from this course, please ask them to complete the activities on page 29 of Abacus Workbook 1.