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Addition and Subtraction
Objectives
To add and subtract single digit numbers using number facts and patterns
Resources
Abacus Workbook 1 | 100 bead string
Vocabulary
number facts | number pairs | addition facts | subtraction facts
Today's Lesson
Introduction
Before you start the lesson, watch this Recap Video with your student.
Show your student 5 beads on a 0-100 beaded line or 100 bead string. Then find 3 more. Ask, ‘What is 5 and 3?’ Say, ‘We know this!’
Show 15 and 3 more. Ask, ‘15 and 3 is?’
Write 15 + 3 and underline the 5 + 3 in one colour. Say, ‘This is the part we know!’
Repeat for 25 + 3, 35 + 3… 95 + 3.
Say, ‘Because we know 5 add 3, we don’t need to count on.’
Repeat to show for 9 – 4 on the 0-100 beaded line, and then to do 19 – 4, 29 – 4… 99 – 4.
Say, We can subtract 4 from any number ending in 9 because we know the answer to 9 subtract 4.
Underline the 9 – 4 in one colour in each subtraction so your student sees this point clearly.
Main Activity
Write 32 + 5 on a whiteboard
Ask your student which fact we need to use to find 32 + 5.
Point out that we need to know that 2 + 5 = 7. Ask why. Expect your student to explain that if we know 2 + 5 = 7 we also know that 32 + 5 = 37.
Say that now these should be quick to calculate:
52 + 5 =
72 + 5 =
92 + 5 =
Can they try these sequences on their own?
7+2=
17+2=
27+2=
How about:
6-3=
16-3=
26-3=
Can they make up their own sequence for 6+2=? How about 9-5=?
Can you invent one together where the units are swapped around, such as 43 + 6.
Extra Support
Use the 100 square for support so that your student can track the patterns visually.
Extra Challenge
Challenge your student to invent sums that cross a multiple of ten, for example, 47 + 5.
Workbook
To help your student consolidate their learning from today, please ask them to complete the activities on page 16 of Abacus Workbook 1.