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Addition and Subtraction
Objectives
To subtract 10, 11, 20 and 21.
Resources
Abacus Workbook 2 | Coins | Small toy spider | 100 square | 0-100 Beaded line | Assignment 2
Vocabulary
ten(s) | multiple(s) of 10 | one(s) | add | subtract
Today's Lesson
Assignment
This lesson works towards Assignment 2. Please access the assignment for details about what you will need to submit to your student's Wolsey Hall tutor.
Introduction
Before you start the lesson, watch this Recap Video with your student.
Recap on Lesson 2 by asking your student to show you how to use Spider and the 100 square to add 10, then add 20, then add 11, then add 21.
If needed, spend some time today reinforcing these skills, especially adding 11 and 21, so that your student is confident and accurate.
New Learning
Say to your student that we can also use Spider and the 100 square to help up with subtracting.
Ask, ‘Can you work out which direction Spider will need to go to subtract? Can you make Spider subtract 10? What about 20? What about 11? What about 21?’
Support your student with this.
Give your student a 2-digit number and practise subtracting 10.
Record the number sentence, for example, 46 – 10 = 36.
Then choose a different 2-digit number and subtract 10, then 11, then 21.
Record all the number sentences.
For example: 34 - 10 = 24, 34 - 11 = 23 and 34 - 21 =13.
Main Activity
Look at Assignment 2 with your student. Read the instruction given at the top of each activity first, and make sure your student understands what they need to do. Please ask your student to write their answers on the printed out assignment sheet.
Complete Assignment 2.
Note: The completed assignment should be submitted to your student's Wolsey Hall tutor at the end of Step 6 Lesson 5.
Extra Challenge
Play this game as a pair with your student.
You should each choose a number between 90 and 100.
Spin a coin. If it lands on heads, you should subtract 11 or 21 or 1.
If it lands on tails, you should add 10.
Take turns to play. Each time, you or your student should spin the coin and record the calculation.
The first person to get to a number less than 5 is the winner.
Play several times.
Then ask your student to calculate the ideal set of coin landings if you were starting from 99, i.e. what would be the fastest route to a number less than 5 if you started at 99?
Workbook
To help your student consolidate their learning from today, please ask them to complete the activities on page 6 of Abacus Workbook 2.