题干

心理学家分析发现视觉和空间能力与性别有关,某数学兴趣小组为了验证这个结论,从兴趣小组中按分层抽样的方法抽取50名同学(男30女20),给所有同学几何题和代数题各一题,让各位同学自由选择一道题进行解答.选题情况如右表:(单位:人)

(1)能否据此判断有97.5%的把握认为视觉和空间能力与性别有关?
(2)经过多次测试后,甲每次解答一道几何题所用的时间在5~7分钟,乙每次解答一道几何题所用的时间在6~8分钟,现甲、乙各解同一道几何题,求乙比甲先解答完的概率.
(3)现从选择做几何题的8名女生中任意抽取两人对她们的答题情况进行全程研究,记甲、乙两女生被抽到的人数为 X,求 X的分布列及数学期望 EX.
附表及公式

K2=
n
a
d
-
b
c
2
a
+
b
c
+
d
a
+
c
b
+
d
上一题 下一题 0.0难度 选择题 更新时间:2019-09-15 05:22:15

答案(点此获取答案解析)

【解答】解:(1)由表中数据得K2的观测值K2=50×22×12-8×<

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    From Dusner (3 speakers) to Kelabit (5 thousand) to Yiddish (1.5 million), these languages are spread, but like the Indian elephant, they are in danger of dying out. Dr. Chris Mazdzer, a researcher at Oxford University, organizing a meeting on endangered languages thinks there could be a novel way to keep minority languages alive: social media. He says, “Because young people text each other how they speak, even if they don't know how to spell it.”

    Minority languages are often at risk of being drowned(淹死)out by the bigger ones, which are spoken at school and in the media. But the appearance of Facebook and Twitter might just have the unexpected effect. Dr. Mazdzer speaks Frisian, which has 350,000 speakers. Communicating with his own language has given him thought about how languages could be saved in the future. “In Friesland, young people who don't learn much Frisian at school send each messages on social media in Frisian”, he says. In this way, a new generation of Frisian speakers keeps the language alive.

    Though many of these languages only have a few speakers, it's not just a small number of speakers that make a language endangered. Some languages were once widely spoken, but lost speakers over time. This can happen for many reasons, like only one language spoken in school or people moving away from their home and losing their language.

    Tweeting and texting in Frisian (or Sorbian, or Breton) is not enough in the long term, though. There are many other things we need to do. But why is a language worth saving in the first place? Because our languages are natural creations. Natural beauty needs to be protected.