Introduction

Mental calculation is  the practice of doing mathematical calculations using only the human brain, with no help from any computing devices (Wikipedia). Mental calculation is said to improve mental capability, speed of response, memory power and concentration.

One way to practice mental calculation is using Abacus System. The Abacus System of mental calculation is a system where users mentally visualize an abacus to do calculations. No physical abacus is used; only the answers are written down. This system is being propagated in Malaysia, South Korea, Thailand, Singapore and Japan.

The Abacus method of mental calculation helps development of the right brain. In this method, the learners manipulate abacus beads in their head to carry out a calculation. Recent studies have proven that the Abacus method of mental calculation is extremely effective in activating the right brain.

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Why Mental Calculation?

Research shows that the vast majority of calculations used in every day life are done mentally. In fact, one study revealed that mental strategies accounted for 85% of all calculations done by adults in their daily life (Northcote & McIntosh, 1999). Mental calculation encourages students to formulate their own range of strategies or techniques and promotes understanding and flexibility in number operations, know as number sense.

Note:Number sense refers to a person's general understanding of number and operations along with the ability to use this understanding in flexible ways to make mathematical judgments and to develop useful strategies for solving complex problems (Burton, 1993; Reys, 1991)

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Some examples of Mental Calculation

Example	Mental calculation	Reason
398*4	1600-8=1592	398*4=(400-2)*4   =400*4-2*4   =1600-8
240*5	120*10 divide by 2 and multiply by 10	240*5=240*10/2   =(240/2)*10   =120*10
320/5	640/10 multiply by 2 and divide by 10	320/5=320/(10/2)   =(320*2)/10   =640/10
760*200	calculate 76*2 and multiply by 1000	760*200=76*10*2*100   =76*2*1000
12*25	3*100 divide by 4 and multiply by 100	12*25=12*(100/4)   =(12/4)*100   =3*100
13*99	1300-13	13*99=13*(100-1)   =1300-13