วิธีการ”คูณ”เลขในใจเร็ว2

25 Nov

2.“วิธีจำผลคูณที่ตรงกลางให้ได้”0” “ ซึ่งสามารถนำไปใช้กับข้อ 1 ได้ครับ เช่น

3×34=102   9×12=108   11×19=209

3×35=105   9×23=207  11×28=308

3×36=108   9×34=306   11×37=407

3×67=201   9×45=405   11×46=506

3×68=204   9×56=504   11×55=605

3×69=207   9×67=603   11×64=704

9×78=702   11×73=803

9×89=801    11×82=802

11×91=1001…ฯลฯ

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