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We can multiply and divide by 10 and 100 up to 2 decimal places
Year 4 Unit 15b
What we are learning:
We can use our knowledge to multiply or divide numbers by 10 or 100 even when they have decimals in them.
The place value chart reminds us of the order of columns and their value:
Thousands, Hundreds, Tens, Units, decimal point, tenths, hundredths
- Remember to emphasise and discuss the fact that to multiply a number by 10 we move the number one column to the left, to multiply by 100 we move it two columns to the left. Where this leaves gaps in the units or tens columns we insert a zero. This is not the same as adding one or two zeros to a number, which does not work for decimals.
- For example, to multiply 3.86 by 10 we move it one place to the left and get 38.6 To multiply 3.86 by 100 we move it two columns to the right and get 386, which could also be written as 386.0
- To divide a decimal number by 10 we move it one column to the right, and to divide by 100 we move it two columns to the right.
- For example to divide 4793 by 10 we move it one column to the right and get 479.3
- To divide 4793 by 100 we move it two columns to the right and get 47.93
Activities you can do at home:
Use a number line or chart like the one above until your child is confident multiplying and dividing decimals by 10 or 100.
Then try asking individual questions without a chart or visual prompt, e.g.
What is 5.7 multiplied by 100? Your child then has to visualise the number and how it moves two columns and say the answer – in this case 570
If your child:
Moves an incorrect number of columns
Use a visual prompt such as a place value chart like the one above so that they can see the columns labelled. Keep using this until your child is confident to work without it.