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问题 解答题

假设每一架飞机引擎在飞行中故障率为1–p，且各引擎是否有故障是独立的，如有至少50%的引擎能正常运行，飞机就可成功飞行，则对于多大的p而言，4引擎飞机比2引擎飞机更为安全？

答案

当引擎不出故障的概率不小于时，4引擎飞机比2引擎飞机安全

飞机成功飞行的概率分别为  4引擎飞机为:

    

2引擎飞机为.

6P2（1–P）2+4P2（1–P）+P4≥2P(1–P)+P2,解得P≥.

即当引擎不出故障的概率不小于时，4引擎飞机比2引擎飞机安全. 

单项选择题

I was a single parent of four small children, working at a low paid job. Money was always tight, but we had a (1) over our heads, food on the table, clothes on our backs, and if not a lot, always (2) . Not knowing we were poor, my kids just thought I was (3) . I’ve always been glad about that.
It was Christmas time, and although there wasn’t (4) for a lot of gifts, we planned to celebrate with a family party. But the big (5) for the kids was the fun of Christmas (6) .
They planned weeks ahead of time, asking (7) what they wanted for Christmas. Fortunately, I had saved MYM120 for (8) to share by all five of us.
The big (9) arrived. I gave each kid a twenty-dollar bill and (10) them to look for gifts of about four dollars each. Then everyone scattered. We had two hours to shop; then we would (11) back at the "Santa’s Workshop"
Driving home, everyone was in high Christmas spirits, (12) my younger daughter, Ginger, who was unusually (13) She had only one small, flat bag with a few candies—fiftycent candies I was so angry, but I didn’t say anything (14) we got home. I called her into my bedroom and closed the door, (15) to be angry again. This is what she told me.
"I was looking (16) thinking of what to buy, and I (17) to read the little cards on the ’Giving Trees’. One was for a little girl, four years old, and all she (18) for Christmas was a doll. So I took the card off the tree and (19) the doll for her. We have so much and she doesn’t have anything. "
I never felt so (20) as I did that day.

二、完形填空

A．improvement

B．problem

C．surprise

D．excitement
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单项选择题 B1型题

脑膜炎球菌属（）

A.志贺菌属

B.奈瑟菌属

C.沙门菌属

D.埃希菌属

E.弧菌属
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