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Subtraction
Objectives
To apply two different methods to subtraction calculations.
To establish which method is most efficient or appropriate to use.
Resources
Abacus 4 Textbook 1 | Squared paper
Today's Lesson
Main Activity
Ask your student to recite two more times tables and to answer random questions on these.
Turn to page 22 in Abacus 4 Textbook 1.
Look at the two columns and ask your student to remind you of how to go about each method.
82 - 47: For the counting up (‘frog’) method, it would be:
47 + 3 = 50
50 + 30 = 80
Then 80 + 2 to reach 82
Answer: 3 + 30 + 2 = 35
95 – 21: Remind your student that counting back (taking away) should only be used if the number being subtracted is very small (1-digit) or it has fewer 10s and 1s than the larger number so the counting back is easy, e.g. 95 - 21
95 count back 20 is 75, then count back 1 equals 74
Answer: 95 – 21 = 74
Watch this video which talks you through the two methods and how it applies to some of the questions on page 22.
Ask your student to copy and complete the page, using the methods specified. In the second section, tell your student they may use their preferred method.