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We can multiply numbers with decimals by a one-digit number using efficient written methods
Year 6 Unit 10d
What we are learning:
- When we are multiplying decimals by a one digit number we can easily use the compact or efficient method that we have learned previously.
- If we have 35.2 x 4 we can estimate our answer by rounding 35.2 to 36 and multiplying this by 4 to make 144 (4 x 30 = 120 and 4 x 6 =24, added together make 144)
- We set the calculation out like this:
Notice how we put the decimal point in the answer underneath the decimal point in the number we are multiplying. We know that our answer is likely to be right as it is near the estimation of 144.
If the decimal point is in a different place, e.g. 3.52 x 4 we still carry out the calculation in the same way, with the decimal points in line with each other.
Now we can see that our estimate would be 4 x 4 = 16 and the answer is 14.08
We can also apply this to multiplying money. If we have 3 x £12.61 we set it out like this:
We know that we are multiplying each value as follows:
3 x 1p; 3 x 60p; 3 x £2 and 3 x £10.
Providing we understand this, in our heads we can say 3×1; 3×6; 3×2 and 3×1 and carry across any answers that have more than one digit.
Activities you can do at home:
In the Activity Sheet you will find examples to work on together that you have to set out for yourselves.
Good questions to ask:
How do we set this out?
Where does the decimal point go in our answer?
What is your estimate of the answer?
How near to the estimated answer is the real answer and what does this tell us?
If your child:
Makes calculation errors when multiplying or adding
Slow down their calculation and ask them to talk it through out loud as they do it – this often helps them identify their own errors and they self correct them as they realise.
If they don’t see their error, ask them Are you sure about that part? This will prompt them to look at it more carefully again.
If they still cannot see their mistake, point it out to them with a question,
e.g. Is that number right?