Year 5

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We can work out sums and differences of numbers with up to three decimal places

Year 5 Unit 3

What we are learning:

  • A key skill is to use what we know to work out what we don’t know rather than attempting to work out a calculation as it is given to us. For example, to calculate double 3.7 we can use the fact that 37 + 37 = 74 and the understanding that because 3.7 is ten times smaller than 37 then the answer will also be ten times smaller (7.4)
  • Similarly if we have 4.5 – 2.9 we can work out 45 – 29 as 16 which tells us that the answer to the calculation we have will be 1.6

Activities you can do at home:

Play “What else do you know?” A game for 2 or more players.
You will need: Pencil and paper and pen for each player

How to play:
1. Players decide on addition or subtraction fact involving two-digit numbers e.g. 54 + 38 = 92
2. Each player writes this fact in the middle of their piece of paper.
3. Each player has to write as many related facts as they can around this fact using decimal numbers and the operations of addition and subtraction only. e.g. 0.54 + 0.38 = 0.92, 9.2 – 3.8 = 5.4
4. After a given time limit, players compare and check calculations.
The winner is the person who has listed the most correct related facts that meet the rules above.
Now repeat the game with three-digit numbers.

Good questions to ask:

Can you find an easier way to do this calculation?
Is there another way you could do this?
Which is the easiest way for you? (this might not be the method you think is easiest!)
What makes this easy for you?

If your child:

Can’t see the links between the question and what they already know
Talk around the question. If they are too focused on the question itself they will not be thinking of what they already know and how it might help them.
Encourage them not to worry about the actual question and ‘getting the right answer’ immediately. Ask them what they know that might be related to the question and prompt them to think more broadly. This is how we all approach problems that we don’t immediately have the solutions for!

Extension Activity

Please use this activity when you think your child understands the unit of work. It will deepen and extend your child’s understanding of this unit.


Extension activity (PDF)