Bobis, Mulligan and Laurie ( 2008) defines mental computation as an ability to mentally calculate addition and subtraction based on knowledge of number facts. In this strategy, it is important for the students to be able to use another alternative to decompose two digit numbers for addition and subtraction. The integration of mental computation skills in early number frameworks enables the development of robust number fact knowledge based on number sense.
In solving the problem, 26 is split up to 20 and 6. Thus, 38 plus 20 equals to 58. We still have six remaining thus 58 plus 6 equals to 64. Beside, the students can as well split the 26 to 10, 10 and 6. By splitting a big number to a small one, it makes thing easier to the students. During the splitting process as well, it is important that the teacher prompt questions like
" why splitting 26 to 10, 10 and 6?",
"it is the still the same if 26 is split to 20 and 6?".
Those kind of questions eventually engages the student's reasoning and critical thinking skills as it gets them to think and viewing thing from different perspective.
Example of 100 chart
In solving problem like 72 - 25 = 47, the student can jump from 72 to 70. 25 is splitting up to 20 and 5, thus from 70, the students minus 20 and land at 50. From there, 50 minus 5, and lands at 45. As the 72 jumped to 70 and take away two, we need to plus two, thus it lands at 47.
* Important note : In hundred charts and number line, there are several strategies involved. They are -splitting to tens backward, or forward,
-jumping to the nearest tens backward and forward
- add numbers if take away
- minus numbers if add on
It is crucial for teachers to address this in engaging the students with hundred charts and number line.
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