笔算．540×15 208×42230×90 506×40．
计算，能简算的要简算．．
食堂运进一批大米，吃掉吨，比剩下的多吨．这批大米原有多少吨？
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看“分数墙”列式计算
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吨，比剩下的多
吨．这批大米原有多少吨？
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