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3546×319=1121174 ； 89×931=82839

错啦！. 3546×319=1121174 ； 89×931=82839. ？. 小丁丁的秘密“武器”. 知识百花筒. 弃九数. 3617 ： 3 ＋ 6 ＋ 1 ＋ 7  1+7=8. 9. 去掉 3 ＋ 6=9 8 为“弃九数”. 9. 3546×319=1121174. 319. 3546.  3+6=9. :3+5+4+6. 9. :3+1+9  3+1=4. 4. 9. 3546×319=1121174. 1121174.  3+6=9. 319. :3+5+4+6. 9. 9. × =36.

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3546×319=1121174 ； 89×931=82839

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  1. 错啦！ 3546×319=1121174； 89×931=82839 ？

  2. 小丁丁的秘密“武器”

  3. 知识百花筒 弃九数 3617：3＋6＋1＋71+7=8 9 去掉3＋6=9 8为“弃九数”

  4. 9 3546×319=1121174 319 3546 3+6=9 :3+5+4+6 9 :3+1+93+1=4 4

  5. 9 3546×319=1121174 1121174 3+6=9 319 :3+5+4+6 9 9 × =36 1+1+2+1+1+7+4  1+1+2+4=8 3+6=9 9 4 4 8 :3+1+93+1=4 3546

  6. 3546×319=1121174 1131174 1131174 9 9 9 9 8 8 1+1+3+1+1+7+4  1+1+3+4=9 4 4 9  = 9

  7. 实践畅想园 一、试一试，用“弃九法”验算 89×931=82839是否正确。

  8. 实践畅想园 二、用“弃九法”验算下列各题是否正确。 （1）228×222＝50616；　 （2）334×336＝112224； （3）46876×9537＝447156412

  9. 商×除数=被除数—余数 “弃九法”能检验有余数的除法吗？ 试一试, (1)37479÷341=109……310 (2)90087÷675=133……552

  10. 想一想： • “弃九法”验算法有没有不足之处？ • 为什么说“原结果可能正确”？ • 有没有方法可以弥补？

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