[题目]甲.乙两门高射炮同时向一敌机开炮.已知甲击中敌机的概率为0.6.乙击中敌机的概率为0.8.敌机被击中的概率为．题目和参考答案——青夏教育精英家教网—

题目内容

【题目】甲、乙两门高射炮同时向一敌机开炮，已知甲击中敌机的概率为0.6，乙击中敌机的概率为0.8，敌机被击中的概率为________．

【答案】0.92

【解析】解法一：设“甲击中敌机”为事件A，“乙击中敌机”为事件B，事件A、B相互独立，所以所求的概率为P＝P(A∩B)＋P(∩B)＋P(A∩)＝P(A)·P(B)＋P()·P(B)＋P(A)·P()＝0.6×0.8＋0.4×0.8＋0.6×0.2＝0.92.

解法二：利用对立事件的概率，P＝1－P(∩)＝1－P()·P()＝1－(1－0.6)(1－0.8)＝0.92.

解法三：敌机被击中为事件A∪B，P(A∪B)＝P(A)＋P(B)－P(A∩B)＝P(A)＋P(B)－P(A)·P(B)＝0.6＋0.8－0.6×0.8＝0.92.

练习册系列答案

68所名校图书小升初高分夺冠真卷系列答案

相关题目

现代乡村旅游是一种新型、绿色的旅游模式，通常是指以田园风光、农庄农场以及乡村民俗文化为主题的观光、休闲及体验式的旅游活动。改革开放以来，随着我国经济的发展，现代乡村旅游业迅速发展。

简述我国发展现代乡村旅游业对于农村地区可持续发展的意义。

【题目】世界范围内，在一些城市不断发展的同时，也有一部分城市面临城市收缩问题。影响我国城市收缩的常见要素有：资源状况、产业活动、地理位置等。据此完成下面小题。

【1】城市收缩易导致的结果是（）

①人口减少②环境退化③空间收缩④交通拥堵⑤经济衰退

A.①②③B.①③⑤C.③④⑤D.②③④

【2】对城市收缩可起到较好抵御作用的是（）

A.高校、大型交通枢纽B.商场、汽车修配厂

C.大型影院、批发市场D.三甲医院、小学校

【题目】某工厂造A、B型桌子，每张桌子需木工和漆工两道工序完成.已知木工做一张A、B型桌子分别需要1小时和2小时，漆工油漆一张A、B型桌子分别需要3小时和1小时；又知木工、漆工每天工作分别不得超过8小时和9小时，而工厂造一张A、B型桌子分别获利润2千元和3千元，试问工厂每天应生产A、B型桌子各多少张，才能使获得的利润最大？最大利润是多少？

【题目】阅读理解

阅读下列短文，从每题所给的四个选项（A、B、C和D）中，选出最佳选项。

On November 18, 1995, Itzhak Perlman, the famous musician, came on stage to give a concert. If you have ever been to a Perlman concert, you know that getting on stage is no small achievement (成就) for him. He suffered from a disease as a child, and so he walks with the help of two walking sticks.

The audience (观众) sat quietly while he makes his way across the stage to his chair and begins his play. But this time, something went wrong. Just as he finished the first few bars, one of the strings (弦) on his violin broke. We thought that he would have to stop the concert. But he didn’t. Instead, he waited a moment, closed his eyes and then signaled the team to begin again.

Of course, anyone knows that it is impossible to play a pleasant work with just three strings. I know that, and you know that, but that night Itzhak Perlman refused to know that.

When he finished, there was a breathtaking silence in the room. And then people rose and cheered. He smiled and said—not proudly, but in a quiet attitude—“You know, sometimes it is the artist’s task to find out how much music you can still make with what you have left.”

This powerful line has stayed in my mind ever since I heard it. And who knows? Perhaps that is the meaning of life—not just for artists but for all of us.

So, perhaps our task in this fast changing, puzzling world in which we live is to make music, at first with all that we have, and then, when that is no longer possible, to make music with what we have left.

【1】What made Itzhak Perlman’s performance at the concert special on November 18, 1995?

A. He just recovered from a serious illness.

B. He was late for the stage.

C. He had a quarrel with the audience.

D. His string of violin got broken.

【2】 Why didn’t Itzhak Perlman accept the fact on the stage?

A. He was a person of pride.

B. He thought the audience didn’t see that.

C. He decided to succeed with bad conditions.

D. He didn’t see the string get broken at all.

【3】 Why did the audience stand up after the performance?

A. They were moved by his spirit.

B. They were moved by his disease.

C. They laughed at his action.

D. They wanted to relax.

【4】 What is the best title for the passage?

A. When you lose the most important thing

B. How can you give it up easily?

C. Playing a violin with three strings

D. Playing a violin to yourself

【题目】如图所示，是某海湾旅游区的一角，其中，为了营造更加优美的旅游环境，旅游区管委会决定在直线海岸和上分别修建观光长廊和AC，其中是宽长廊，造价是元/米，是窄长廊，造价是元/米，两段长廊的总造价为120万元，同时在线段上靠近点的三等分点处建一个观光平台，并建水上直线通道（平台大小忽略不计），水上通道的造价是元/米．

（1）若规划在三角形区域内开发水上游乐项目，要求的面积最大，那么和的长度分别为多少米？

（2）在（1）的条件下，建直线通道还需要多少钱？

（1）若规划在三角形区域内开发水上游乐项目，要求的面积最大，那么和的长度分别为多少米？

（2）在（1）的条件下，建直线通道还需要多少钱？

【题目】The Harrington School is an old one-room schoolhouse in Georgia. The building has not been used in years. Community leaders and even the local historical society thought it wasn’t worth saving. “Just look at it and you could tell it was going to fall any minute, so let’s tear it down, ” they said.

The Harrington School was built in nineteen twenty-five for black children on St. Simons Island. Amy Roberts well remembers she attended first grade there in nineteen fifty-three. That was a year before the United States Supreme Court ruled that schools had to be racially integrated. A number of states kept blacks from attending school with whites. After the ruling, the children joined white students at St. Simons' other elementary school.

The old schoolhouse continued to be used for social activities and a day care center. By 1970, however, it was empty. Amy Roberts worried that developers might tear it down. So she started the African-American Heritage Coalition to try to save it.

“If it's not saved, then eventually you would not know that we existed here on St. Simons. Everything of African-American heritage has been torn down，” she said.

In 2009 the Harrington School was weeks away from destruction. Then a local historian named Patty Deveau took a closer look. She remembered a movement called the Rosenwald Fund.Georgia historian Jeanne Cyriaque explains, “At the very core of that movement was the involvement of the community, sympathetic whites and philanthropy, merging together to do what today we'd call partnerships.”

Julius Rosenwald was a businessman. In 1915 he donated money to black communities to build their own schools. By the late 20s, the Rosenwald Fund had donated to more than 5,000 educational buildings in 15 states across the South. One-third of rural black children were attending a Rosenwald school.

“This particular school kind of embodies to me what was going on with the communities at the time, because in many African-American communities, it was African-American families that gave land for these schools to be built.” Jeanne Cyriaque said.

Now, preservation architects are developing plans to restore the Harrington School. Amy Roberts and others were surprised by what the experts found about the structure. “They went through it and they talked about how sound it was and how, you know, I mean, they'd never seen anything like this. I mean, it was, like, in great shape!”