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Mental computation

MC_GT_T1_E2_A2_fig1

The problem 24 minus 8 solved by subtracting 4 from 20 and then adding 4, with a diagrammatic representation.

Screen grab from L97 The takeaway bar: make your own easy subtractions.
Source: © Education Service Australia, 2011.

MC_GT_T1_E3_A1_fig1

Problem of 60 plus 40, broken into 60 plus four lots of 10, with a diagrammatic representation.

Screen grab from L92 The part-adder: make your own hard sums.
Source: © Education Services Australia, 2011.

MC_GT_T1_E3_A1_fig2

Problem of 90 minus 30, with a diagrammatic representation.

Screen grab from L98 The take-away bar: make your own hard subtractions.
Source: © Education Services Australia, 2011.

MC_GT_T1_E3_A2_fig1

Using a number line to add 43 and 50.

Screen grab 1 from Number line applet.
Material from NZ Maths website published by the New Zealand Ministry of Education. Reproduced with permission from the New Zealand Ministry of Education © Crown.

MC_GT_T1_E3_A2_fig2

Using a number line to subtract 50 from 137.

Screen grab 2 from Number line applet.
Material from NZ Maths website published by the New Zealand Ministry of Education. Reproduced with permission from the New Zealand Ministry of Education © Crown.

MC_GT_T1_E3_A3_fig2

Using a number line to subtract 63 from 127, first subtracting 60 and then subtracting 3.

Screen grab from Number line applet.
Material from NZ Maths website published by the New Zealand Ministry of Education. Reproduced with permission from the New Zealand Ministry of Education © Crown.

MC_GT_T1_E3_A4_fig1

A string of beads, alternating every ten beads from green to pink. The problem is to add 27 to 58. First peg is at 58 with a jump of 20 to reach 78, then a jump of 2 to reach 80 then a jump of 5 to reach the answer of 85.

Adding with a bead string (solution 1).

MC_GT_T1_E3_A4_fig2

A string of beads, alternating every ten beads from green to pink. The problem is to add 27 to 58. First peg is at 58 with a jump of 2 to reach 60, then a jump of 5 to reach 65 then a jump of 20 to reach the answer of 85.

Adding with a bead string (solution 2).

MC_GT_T1_E5_A1_fig1

Problem of 62 minus 28, with a diagrammatic representation of 28 added to 30 to give 58, leaving 4 to reach 62.

Screen grab from L112 The difference bar: generate hard differences.
Source: © Education Services Australia, 2011.

MC_GT_T1_E5_A1_fig2

Problem of 62 minus 28, with a diagrammatic representation of 2 added to 28 to give 30, leaving 32 plus the remaining 2 to reach 64.

Screen grab from L110 The difference bar: make your own hard subtractions.
Source: © Education Services Australia, 2011.

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