Programme 10: Plus and minus
- Recognising subtraction as the inverse of addition
- Checking by inversion (e.g. checking subtractions by adding or using known number facts)
- Subtracting a teens number from a two-digit number by partitioning
Vocabulary: subtract, subtraction, minus, check, add, addition, plus, couple
Resources: cubes, cloth, counters, Make a path resource sheet
Encourage children to recognize that the = sign is a balance between each side of an equation i.e. number sentences can be written 4 + 8 = 12 or 12 = 4 + 8 [or as a subtraction 12 - 8 = 4 or 4 = 12 - 8].
Number sentences Whole class or group work
Write three (related) numbers e.g. 11, 8, 3 and ask the children to make up number sentences using these numbers. Explore all the different combinations they can find.
8 + 3 = 11, 3 + 8 = 11, 11 - 8 = 3, 11 - 3 = 8 and related multiples of 10.
Encourage the children to recognize that if they can use their knowledge of number bonds to work out addition and subtraction and to check their calculations.
How many are hidden? - Whole class or group work
Ask one child to scoop up some cubes and count them. One person secretly hides some of the cubes under a cloth and the other children have to try and work out how many are hidden. Check by adding the hidden cubes to the seen cubes. Discuss the methods children use to calculate the number of hidden cubes.
E.g. Total cubes 21 - [ ] = 8 can be calculated in different ways - counting on from 8 to 21, counting back 8 from 21, knowing that 8 + 12 = 20 therefore 8 + 13 = 21 etc.
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