某试卷共有20题选择题，对于每道题选对得10分，不选或错选倒扣5_爱下问搜题

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问题解答题

某试卷共有20题选择题，对于每道题选对得10分，不选或错选倒扣5分，则至少要选对几道题得分才能不少于80分？

答案

设至少做对x道，

依题意得：10x-5（20-x）≥80

解得：x≥12．

答：至少要选对12道题得分才能不少于80分．

完形填空

After the quake hit northeast Japan on March 11, many moving stories that I saw with my own eyes happened around me.
I had to walk home since all the 41 had stopped after the earthquake. On my way home I 42 an old lady at a bakery shop who was giving out free bread, which made my heart 43 . A man was holding a sign that said, “Please use our 44 .” He was 45 his house for people to go to the restroom.
My friend wanted to 46 others. He stood in the cold with a sign “If you’re okay with a motorcycle, I will 47 you to your house.” And then I saw him take one gentleman home, all the way to a faraway place!
Then next day I drove to 48 my car with gas. There is a lack (缺乏) of 49 now and many gas stations are either closed or have very 50 lines. I got 51 , since I was behind 15 cars. Finally, when it was my 52 , the man smiled and said, “ 53 this situation, we are only giving $30 worth gas per person. Is that alright?” “ 54 . I’m just glad that we are all able to 55 ,” I said. His smile gave me so much comfort.
I saw a man at the evacuation (疏散) center 56 when people brought food to him. It was the first time in three days that food was brought to their center. However, after he wiped the tears, his next 57 surprised me. “I am very 58 that we are provided with food. But people in the city next to us haven’t 59 any food at all. Please go to that center as well.” And when hearing that, I realized there is a bright future on the other side of this 60 .

A．information

B．Together with

单项选择题

设随机变量X与Y相互独立，且均服从正态分布N(0，1)则______．

A．P(X+Y≥0)=1/4
B．P(X-Y≥0)=1/4
C．P(max(X，Y)≥0)=1/4
D．P(min(X，Y)≥0)=1/4