Mental calculation technique

Mental calculation technique

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 76*2*2000 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
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April 12th, 2007
Filed under: Maths |

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