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We can multiply up to four-digit numbers by a two-digit number using an efficient written method
Year 5 Unit 12b
What we are learning:
Now we can extend the efficient method to multiply a two digit number by another two digit number, such as 56 x 27
First we multiply 56×7 as we have done before in Unit 12a. This part is shaded so that you can see it clearly.
Then we multiply 56×20. This part is shaded below.
When we multiply 56×20 it is easier to multiply 56×10 first (i.e. slide the answer one place to the left by inserting a zero placeholder in the units column), and them multiplying by 2 (because 10×2=20).
Now add the two answers together to find the final answer.
Remember to carry value across each row of multiplication – you can only put one digit in each column!
When your child becomes confident with this process, then we use exactly the same format for multiplying higher numbers e.g. 1236 x 24
First we multiply 1236 by 4 (shaded area above)
Then we multiply 1236 by 20
Then we add the 2 answers together.
ACTIVITY 1: MULTIPLICATION EXPANDED METHOD
ACTIVITY 2: MULTIPLICATION SHORT (EFFICIENT) METHOD
Activities you can do at home:
Building up confidence in long multiplication takes time and practice. It is important that your child understands what they are doing at each stage of the calculation. Of course, they will also need to be very confident with their
Have a go at the examples provided and talk each stage through together.
It is essential that calculations are set out neatly in columns; otherwise it will not be possible to check that digits are in the correct columns. Using squared paper can help you achieve this easily.
Good questions to ask:
Where are we going to start this calculation?
Which bit are we going to do first?
Have we set the calculation out correctly in the right columns?
Why do we insert a zero first when we are multiplying by the ten?
If your child:
Loses track of the sequence of multiplication activities in the calculation
Make sure that they are confident multiplying two digits by one digit first (Unit 12a). Discuss how we repeat this as the first step when we are multiplying a two digit number by a two digit number. Now explore the second stage. Take each step slowly to see where any confusion is arising.