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We can multiply by 10 or 100 and say what happens to the number we multiply
Year 3 Unit 9
What we are learning:
- When we multiply by 10 the original number gets ten times bigger. All the digits move one place to the left (the units digit moves to the tens, the tens digit moves to the hundreds etc) and we write zero in the units as a ‘place holder’ – without the place holder the original number would appear unchanged.
- When we multiply by 100 the original number gets one hundred times bigger. All the digits move two places to the left (the units digit moves to the hundreds, the tens digit moves to the thousands etc) and we write zero in the units and tens as a ‘place holder’ – without the place holder the original number would appear unchanged.
- It is tempting to say to children “to multiply by 10 add a zero” .This sentence can cause confusion when your child learns to multiply decimals by 10.
1.62 x 10 does not become 1.620 but 16.2
Note that the decimal point does not move, nor do we add a zero. The correct understanding we are seeking is that we move our number across the columns.
ACTIVITY 1: MULTIPLYING BY 10 AND 100
Activities you can do at home:
Use the Place Value grid provided on the “x10 x100” sheet. Use the provided digit cards to make a 1-digit number (then move onto 2-digit numbers). Let your child physically move the digit to the left to multiply by 10 then put the place holder 0 in the correct column. Repeat for multiplying by 100.
Once your child is confident to multiply by 10 and 100 using the “x10x100” sheet, ask them to explain to you what they are doing and why.
Get your child to stand at one end of your largest room. Say a number to them (1-digit or 2-digit dependent on their confidence level) and tell them whether to multiply by 10 or 100. If they answer correctly they move forward one step. Play until they reach you. Switch roles – now get your child to say the numbers and what they should be multiplied by!
Good questions to ask:
How many times is 60 bigger than 6?
How many times is 600 bigger than 6?
What number is ten times bigger than 30?
If your child:
Wants to simply add a zero on the end of the number to multiply by 10
Show them the impact of this on a place value chart – we are moving the number, not adding an extra column!