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Multiplication & Division
Objectives
To quickly multiply by 10 and 100 and to see the connection between multiplication and division.
Resources
Abacus 4 Textbook 3 | Squared paper | Assignment 9
Today's Lesson
Main Activity
For the mental warm ups, call out a few random 3 digit numbers and ask your child to add them mentally.
For example:123 + 200 =
240 + 130 =
Look at page 83 in Abacus 4 Textbook 3 with your student.
Talk about possible strategies for how to multiply larger numbers by 11 and 12.
You could use the grid method, or expanded methods, but these could take quite a long time.
Suggest that an alternative method to try could be multiplying the number by 10, then adding the number once more for multiplication by 11 or twice more for multiplication by 12.
Watch this video which talks you through the strategies of multiplying by 11 and 12 (as outlined below).
Example 1: 23 x 11:
Step 1: Solve 23 x 10 = 230
Step 2: Add 23 to Step 1 230 + 23 = 243 (By adding one more 23 onto 230, this will give me 11 groups of 23 altogether.)
So 23 x 11 = 243
Example 2: 23 x 12:
Step 1: Solve 23 x 10 = 230
Step 2: Solve 23 + 23 = 46
Step 3: Add 46 to Step 1 230 + 46 = 276 (By adding two more 23s onto 230, this will give me 12 groups of 23 altogether.)
So 23 x 11 = 243
Another method for multiplying by 12 could be to multiply the number by 10, then by 2 and then adding the two answers together.
Encourage your student to work the calculations out by using the method of multiplying by 10 first, and then adding the rest.
Please note: the remaining pages in the textbook may be used for revision purposes.
Now complete Assignment 9.