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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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