Numeracy

In Room 12 we have learnt how to use a range of addition and subtraction strategies.

Addition: Place Value Strategy - Holding the biggest number

(Hold the biggest number and add the parts of the other number.)

E.g. 57 + 47 = 57 + 40 + 7

                   = 97 + 7

                   = 104

E.g. 13.4 + 1.3 = 13.4 + 1 + 0.3
                           = 14.4 + 0.3
                           = 14.7

 Addition: Rounding and Compensating strategy
(One number is rounded up or down to a 'tidy ten'. An equal amount must then be taken away or added to the other number to balance the equation.)

E.g.       63 + 59 = 62 + 60
               -1    +1
                            = 122

E.g.       5.2    +    3.9 = 5.1 + 4.0
              -0.1      +0.1  
                                     = 9.1
           

Subtraction: Place Value Strategy
(Break the second number into its parts and take each part away in turn.)

E.g.      47 - 34 = 47 - 30 - 4

                           = 17 - 4

                        = 13

E.g.      4.7 - 3.4 = 4.7 - 3 - 0.4
                            = 1.7 - 0.4
                            = 1.3

Subtraction: Advanced Place Value Strategy

E.g.      82 - 19 = 82 - 10 - 9

                        = 72 - 9 (The nine is split into parts to make this step easier)

                        = 72 - 2 - 7

                        = 70 - 7

                        = 63

E.g.      5.2 - 3.8 = 5.2 - 3 - 0.8
                            = 2.2 - 0.2 - 0.6
                            = 2 - 0.6
                            = 1.4

Subtraction: Equal Adjustment Strategy
(Add an equal amount to both parts of the equation to make the second number tidy.)

Eg.       123 - 49 = 124 - 50

             +1     +1 

                           = 74

E.g. 14.3 - 8.7 = 14 - 9
-0.3 +0.3
= 5

Subtraction: Reversibility Strategy 

(A subtraction equation can be reversed and made into an addition problem. A number line can then be used to help solve the problem)

Eg. 73 - 29 = ?

29 + ? = 73

29    30             70       73

    +1       +40          +3

29 + 44 = 73

so 73 - 29 = 44

Eg. 7.3 - 2.9 = ?

2.9 + ? = 7.3

2.9          3.0             7.0            73

     +0.1          +4              +0.3

2.9 + 4.4 = 7.3

so 7.3 - 2.9 = 4.4