（09年西城区抽样文）为了了解在一个水库中养殖的鱼的有关情况，

（09年西城区抽样文）为了了解在一个水库中养殖的鱼的有关情况，从这个水库的不同位置捕捞出n条鱼. 将这n个样本分成若干组，若某组的频数和频率分别为30和0.25，则n=___________

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（09年西城区抽样文）为了了解在一个水库中养殖的鱼的有关情况，

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