试题与答案

甲、乙两同学参加数学竞赛培训,现分别从他们在培训期间参加的若干次预赛成绩中随机抽

题型:解答题

题目:

甲、乙两同学参加数学竞赛培训,现分别从他们在培训期间参加的若干次预赛成绩中随机抽取8次,具体成绩如下茎叶图所示,已知两同学这8次成绩的平均分都是85分.
(1)求x;并由图中数据直观判断,甲、乙两同学中哪一位的成绩比较稳定?
(2)若将频率视为概率,对甲同学在今后3次数学竞赛成绩进行预测,记这3次成绩中高于80分的次数为ξ,求ξ的分布列及数学期望Eξ.
9875
8x2180035
539025

答案:

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     I am especially interested in eco-friendly cars. Would you please give me some help? 

                                                                                                                                         -John Lily

John Lily,

     More and more automobile companies are taking measures to create cars that do less harm to the planet.

Here are some of the top green cars this year.

Tesla Roadster

     This is an electric sports car. You can travel 220 miles before recharging the battery. The only problem?

It will cost you $ 100 000. So, until you win the lottery or happen to find a box of gold at the end of a

rainbow, let's move on to the more reasonable choices.

Aptera 2e

     This electric car is much more affordable than the Tesla Roadster, with a starting price of around $ 25000.

Its electric motor runs 100 miles per charge. Unfortunately, it is currently only available in California through

a complex booking process.

Toyota Prius

     At 51 miles per gallon in the city and 48 0n the highway, the Toyota Prius is one of the most fuel-efficient

cars in the world. With an annual CO2 rating of 1968 kilograms, this car holds the first place on MSN's list of

the Least Polluting Vehicles of 2009. It also has other eco-friendly features like a solar-powered ventilation (通

风) system. 

Honda Civic Hybrid (混合动力车)

     The Honda Civic Hybrid is competitive with the Toyota Prius when it comes to fuel efficiency. It gets 40

miles per gallon in the city and 45 on the highway. It also has the second- lowest annual CO2 figure, releasing

2160 kilograms in a year.

Honda Insight Hybrid

     With a base price of just $20 000, the Honda Insight Hybrid is the least expensive Hybrid on the market

today. Coming just after the Honda Civic and Toyota Prius in terms of pollution, this fuel-efficient vehicle gets

40 miles per gallon in the city and 43 on the highway.

     Besides all these, Toyota Camry Hybrid is also a good choice. 

                                                                                                                                                 William

1. Compared with Aptera 2e, Tesla Roadster _____.[ ]

A. costs less

B. needs more time to be recharged

C. is harder to book

D. runs much further per charge

2. Which of the following vehicles causes the least pollution to the environment? [ ]

A. Honda Civic Hybrid.

B. Toyota Prius.

C. Honda Insight Hybrid.

D. Toyota Camry Hybrid.

3. We can infer from the passage that _____. [ ]

A. as long as you have won the lottery, you can buy Tesla Roadster

B. only people in California are allowed to buy Aptera 2e

C. Honda Insight Hybrid may be the third least polluting hybrid of 2009

D. the fuel efficiency of the Aptera 2e must be the highest of all the vehicles mentioned

4. What might William be according to the passage? [ ]

A. A future car buyer.

B. A car expert giving advice to people online.

C. An eco-friendly car repairer.

D. An eco-friendly car designer.

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