Year 5

We can explain what calculations we keyed into the calculator and why

Year 5 Unit 13

What we are learning:

• To develop confidence in using a calculator your child needs lots of opportunities to use one. Most mobile phones have a calculator so there is normally one at hand. For example, encourage your child to use their calculator to work out which is the best buy in the supermarket when there are multi-buy offers.
• Make sure that your child has experience of inputting decimal numbers and amounts of money into a calculator and ask them what they notice when they input £56.70 – discuss why the calculator records this as 56.7.
• Add or subtract money on a calculator for example:
  £84.58 – £38. 28 ~ the calculator will display the answer as 46.3 and the child needs to interpret this in terms of the context of the original question – in this case money.
  £67.23 + £28.57 ~ the calculator will display the answer as 95.8 ~ How
  will you record this answer? (it should be £95.80)

Activities you can do at home:

Play ‘Changing digits’
You will need: one calculator

How to play:
1. Put a six-digit number into a calculator for example 123576

2. You must change each digit into a zero in as few turns as possible.

3. You can only use the following keys each time ~ one number key, the +
key and the zero as many times as you like

• Record the steps you take each time
• 123976 + 4 so that the calculator displays 123580
• + 20 so that the calculator displays 123600
• +400 so that the calculator displays 124000 etc

4. Change all the digits to zero until you have changed all the digits except
the one on the left – the number may become too big for the calculator

5. Now try reducing the number to zero by subtracting ~ only use the
following keys – one number key, the – key and the zero as many
times as you like

• Start with 850318 and record the steps you take
• 850318 – 8 so that the calculator displays 850310
• This time you can reduce the digits to zero in any order. To make this into more of a game turn over shuffled digit cards one at a time and reduce that digit to zero.
• Ask What is the value of this digit?
  What will you input into the calculator to reduce this digit to zero?

6. Take it in turns so that your child is also checking what you do – they
will learn from this too.

7. Try again with decimals: 491.312

Good questions to ask:

What number did we start with?
Which digit in the number has turned into a zero?
What did I do to turn this digit into a zero?
Did I add or subtract?
How much did I add or subtract?

If your child:

Gets confused as to how to change the number to zero in a column
Look carefully at the number together and discuss the digit they are trying to change to zero – what value does it have? How much needs to be added to it to turn it to zero?