Feel free if necessary to use a number line or a 100 square to begin with. What we try to focus on for these, and what is more helpful in the long-term, is thinking about what we do know to work out what we don't know. For example we know that :
6 - 2 = 4, and so,
36 - 2 = 34
76 - 2 = 72 and so on.....
Complete pages 16 and 17 of NHM booklet ‘Addition and Subtraction to 100’
An excellent interactive 100 square resource is ‘Splat Square’ that can be accessed through the primarygames website. P3s are very familiar with it. It is very helpful when looking at sequences and patterns in Maths.
Please use 'Splat Square' to practise subtracting 10 from a 2-digit number. This will be very helpful for visual learners. Repeated subtraction of 10 eg:
72 - 10 = 62
62 - 10 = 52
52 - 10 = 42.....and so on will help the children to see patterns and will ultimately help when taking tens numbers (ie 20, 30, 40 etc) from a two digit number.
After lots of practise with this and lots of discussion about patterns that have emerged (ie taking one ten and no units) your P3 will be ready to complete pages 18 of NHM 'Addition and Subtraction to 100'.
Children should have practice subtracting mentally from a two-digit number. This includes taking away a single digit, ten and then a 'teens' number.
Please avail of our Sumdog membership and personal logon details (in green folder from school).
Useful Apps for mental subtraction that we use in the classroom are: