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Mental computation

MC_GT_T1_E5_A2_fig1

A pair of counting strips marked from 1 to 15, the upper one showing the difference between 8 and 13 and the lower the difference between 10 and 15. Finding the difference between 8 and 13 is harder than finding the difference between 10 and 15.

MC_GT_T1_E5_A2_fig2

A pair of counting strips marked from 1 to 15, the upper one showing the difference between 8 and 13 and the lower the difference between 10 and 15. Each has a difference of 5.

MC_GT_T1_E5_A2_fig34

Sets the problem of working out the difference between 27 and 63 and suggests that the solution be in the form of 27 + ? = 63.

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

MC_GT_T1_E6_fig1

Beginning at 203 then subtracting 80 to reach 123, then 7 to reach the result of 116.

Number line for 'result unknown' problem.
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_E6_fig2

First number line showing jump from 74 to 135. Second number line showing jump from 218 to 153.

Number lines for 'change unknown' problems.
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_E6_fig3

Number line showing 56 subtracted from an unknown point to reach the result of 37.

Number line for a 'start unknown' problem.
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_T2_E1_A3_fig1

How many tiles do I need? A partial 6 by 5 array showing only the far left column and top row.

MC_GT_T2_E1_fig1

Six eggs in a carton arranged in a 2 by 3 array.

An array of eggs.

MC_GT_T2_E1_fig2

25 juice boxes arranged in a 5 by 5 array.

An array of juice boxes.

MC_GT_T2_E1_fig3

16 chocolates arranged in a 4 by 4 array.

An array of chocolates.

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