Year 6

We are revisiting how to multiply or divide numbers by 10, 100 or 1000

Year 6 Unit 3

What we are learning:

• When we multiply by 10 it is tempting to say ‘you just add a zero’, but this does not promote understanding of the mathematics. Your child needs to know what is happening to the size of the numbers. Also, adding a zero will only work when multiplying whole numbers, it does not work for decimals
  i.e. 4.7 x 10 is 47 not 4.70
• Similarly, you may have heard the phrase ‘move the decimal point’, however, the decimal point does not move, the digits (numbers) do.
• When multiplying by 10, 100 or 1000, etc, the digits move to the left, as the number is getting larger.
• When dividing by 10, 100 or 1000, etc, the digits move to the right, as the number is getting smaller.
• When multiplying or dividing by 10, move the digits one place in the relevant direction, when multiplying or dividing by 100, move the digits two places in the relevant direction, and when multiplying or dividing by 1000 move the digits three places in the relevant direction.
• Use a place value chart and digit cards to model what happens to the digits.
• Your child also needs to understand that we use zero as a ‘place holder’ e.g. if we multiply 3.2 by 100, all of the digits move two places to the left, however, we need to insert a zero into the units column to show that the answer is 320 and not 32 
  
  Children can get confused by which way the digits ‘move’. Encouraging them to think about what is happening to the size of the number will help with this.

ACTIVITY 1: WHAT DID I DO?

ACTIVITY 2: SECRET CALCULATOR

Activities you can do at home:

Play the game ‘What did I do?’
Write down a list of numbers such as:
0.84    8.4    840    84,000    84     0.084     840,000
Pick two numbers and ask your child to explain how to get from one number to the next e.g. to get from 0.84 to 8.4, you multiply by 10.

Play the ‘Secret Calculator’ Game. A game for 2 players.
You will need: a calculator
How to play:
1. Player 1 enters a number into calculator and passes to player 2.
2. Player 2 has to secretly multiply or divide the number by 10, 100 or 1000 before passing back to player 1.
Player 1 has to work out what player 2 entered into the calculator and say what happened to the number. E.g. ‘you pressed ÷ 100 which made the number 100 times smaller’

Good questions to ask:

Has the number got bigger or smaller? By how many times, 10, 100 or 1000?
How do we know that this number is 10 (or 100, or 1000) times bigger/smaller than the one we started with?

If your child:

Gets confused about the scale of the change between two numbers when multiplying or dividing by 10, 100 or 1000
Make a place value chart on a piece of paper (as in the diagram above) and use small cards with the digits on them that you need. Place the original number on the chart together and then move it physically to its new position.
That way you will be able to see whether it moves to the left (multiplication) or the right (division) and by how many columns. Don’t forget to put the zero placeholder in if it is needed.