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Addition and Subtraction
Objectives
To subtract 2-digit numbers by subtracting multiples of 10 then ones.
Resources
Abacus Workbook 1 | Counters (or plastic fly and spider) | 📄 Subtracting 2-digit numbers | 📄 100 square
Vocabulary
subtraction | tens | ones
Today's Lesson
Introduction
Show your student the 📄 100 square.
Say that Spider and Fly have come back to help us with some subtraction problems.
Write 54 – 23 on paper and ask, ‘Where do we need to position Spider to start with?’ (54)
Now ask: ‘Will she have to jump up or down the 100- square?’
Say that first we need to subtract 20 by jumping back 10 to 44 and then another 10 to 34 (explain that they can do this in one big step if they feel confident). Then to finish the subtraction we need to use Fly.
Count back with Fly another 3 to end up on 31.
Repeat with other subtractions, for example, 86 – 32 and 77 – 25, modelling the subtractions using Spider to count back in tens and Fly to count back in ones.
This video will demonstrate using the 100 square, Spider and Fly to help subtract 2-digit numbers in this way.
Main Activity
Ask your student to complete 📄 Subtracting 2-digit numbers.
They should use counters as Spider and Fly (or an actual plastic spider and fly).
Ask them to place Spider on the larger number and jump Spider back 10 and then back another 10.
Encourage them to do this in one big step after a couple of turns.
They should then slide Fly back 3 spaces and see which number they end up on.
They should record the number sentence, for example: 47 – 23 = 24.
Workbook
To help your student consolidate their learning from today, please ask them to complete the activities on page 53 of Abacus Workbook 1.