小数第１位×小数第１位のかけ算（型分け）

小数のかけ算

小数のかけ算は、整数のかけ算の理解の上に成立しますから、整数のかけ算が理解されている必要があります。
指導の順番としては、\square.\square\times\squareのような×整数を先行させると、小数点をそのまま下ろせば良いというように、加減法と混同してしまう生徒が出ても不思議ではありません。
ここでも一般から特殊へという大原則通り指導します。

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指導の道筋

小数を帯小数、真小数、整数というように型分けをしてみると、次のような８組の型分けができます。

(1) 帯 × 帯 (2) 帯 × 真 (3) 真 × 帯 (4) 真 × 真
(5) 整 × 帯 (6) 整 × 真 (7) 帯 × 整 (8) 真 × 整


小数のかけ算の型分け

(1) 帯小数×帯小数
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(2) 帯小数×真小数
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(3) 真小数×帯小数
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(4) 真小数×真小数
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(5) 整数×帯小数
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(6) 整数×真小数
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(7) 帯小数×整数
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(8) 真小数×整数
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