一堆煤，平均每天用5吨，10天用去多少吨？
直接写得数．﹣=+=+=+=﹣=﹣=﹣=+= 1﹣=﹣=．
计算下面各题．+﹣+++﹣﹣（+）
﹣=+=﹣=﹣=+=﹣= 1﹣=﹣=﹣=+=
+++．
递等式计算+=+=﹣=﹣= 1﹣=+﹣= 1﹣+．
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