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思维训练：口+O+Δ=19，O+O+Δ+Δ=18，口+口+Δ=25；求口，O，Δ
等量代换：口+O+Δ=19，O+O+Δ+Δ=18，口+口+Δ=25；求口，O，Δ
小学《等量代换》，提升数学核心素养7/16
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