采用简单随机抽样，从含有20个个体的总体中抽取一个容量为5的样本，则这个总体中的每个个体被抽到概率都是 ______．
由题意知本题是一个等可能事件的概率，
试验发生包含的事件是从含有20个个体的总体中抽取一个，共有20种结果，
满足条件的事件是从5个个体中选1个，共有5种结果，
∴满足条件的事件是
=5 20
，1 4
故答案为：
．1 4
| 完形填空。 | ||||
| I still remember father spent plenty of time teaching me how to pronounce a word, how to understand something that I saw for the first time and how to be polite to others. And I will never __1__ one sentence my father used to say to me, "I love you, son. Say you love me, son." __2__, I would scream, "I love you, Dad." When I was growing up, I found that I had little in __3__ with my father gradually. Sometimes we often argued about something sharply and then the argument changed into a __4__. I knew there was a gap bet ween us. I didn't __5__ hearing the words "I love you" from my father the last time. To tell you the truth, I couldn't honestly remember when I had last said those words to him, either. Now father was in hospital. The doctor said it was __6__ and he needed an operation at once, __7__ he wasn't sure whether my father was able to survive (幸免于, 经受得住) it. Everything in my childhood __8__ in my mind. Then I called and said, "Dad, I love you!" There was a __9__ at the other end and he replied coldly, "Well, I love you, too!" I cried and said, "Dad, I know you love me, and when you are __10__, I know you will say what you want to say." Fifteen minuets later my mother called and nervously asked, "Paul, is everything OK?" A few weeks later I was working when I received my father's call, "Paul, I love you." I was so __11__ that my tears rolled down my cheeks. Perhaps both of us __12__ that this special moment had taken our relationship to a new level. A short while after this special moment, my father finally narrowly escaped death following the heart operation. I can't __13__ that if I did not take the first __14__ and Dad did not survive the surgery, what kind of life I would lead now. | ||||
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