看看 乘法 如何算

來源：http://www.youtube.com/watch?v=4s77gXFgSEo

what about make it to the neaerst round digit and substract the difference X multiplier?

Like ... 29 X3 = 30X3 -3=90-3=87

7X150 + 6X7 =15X7X10 +42 = 1050+42 = 1092

(in which 15X7 is further calculated as 7X10+7X5 70+35 or even if you byheart multiplication table of 15...like we did in our school)...

12X38 = 12X40- 12X2 = 480-24 = 456...all by mental calculations, when you use grid, you need to carry a paper and pencil ...well, its all about 'Habits' right|?

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