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# Year 4

### We can multiply and divide by 10 and 100.We can explain what happens to the digits when we do this.

#### 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 divide by 10 the original number gets ten times smaller. All the digits move one place to the right (the thousands digit moves to the hundreds, the hundreds digit moves to the tens, the tens digit moves to the units).
• 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.
• When we divide by 100 the original number gets one hundred times smaller. All the digits move two places to the right (the thousands digit moves to the tens, the hundreds digit moves to the units).
• It might be tempting to teach children to multiply by 10 by saying “to multiply by 10 add a zero”. This is incorrect and can cause confusion when your child learns to multiply decimals by 10.
1.62 x 10 does not become 1.620 but 16.2.

#### Activities you can do at home:

Use the Place Value grid provided on the “÷10 ÷100” sheet. Use the provided digit cards to make a 3-digit multiple of 10 (320, 450..).
Move onto 4-digit multiples of 100 (3200, 4500 …) to practice ÷100 when your child is ready.
Let your child physically move the digits to the right to divide by 10.

Once your child is confident to divide by 10 and 100 using the “÷10 ÷100” sheet, ask them to explain to you what they are doing to the digits and why.

What happens to a number when you multiply it by 10
What happens to it when you multiply it by 100?
What do you think might happen to a number if we multiplied it by 1000?

Moves numbers the wrong way when multiplying or dividing
Look at their answers with them and ask whether the correct answer should be bigger or smaller. Then ask them to read the answer from the Place Value Grid. They should begin to see where they have gone wrong. Remember,
moving a number one column to the right makes it ten times smaller, moving it one column to the left makes it ten times bigger.