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×<

同类题2

完形填空

    It impressed me a lot, I never thought that little help will turn out to be the most satisfying thing I have ever done.

    One day I met a man on my way home. He was tired, and1 to climb further. With a broad2 he asked if I could help him with some money. He was paralyzed (瘫痪) in both legs and was 3 funds for some operation. He said that if operated successfully, he could 4a training guaranteeing him a job. I was full of 5 and even asked him to show his legs. I gave him the6 money. After a few days, he again came at my doorstep asking for more money for accommodation. This time I was more or less 7 he is not cheating me. I gave him some and said this is all I have.

    A year went by and I had moved to a(n)8 place. One fine day I got a call from an unknown number. Caller called out his name but I didn't 9 him. Then he said he is the very paralyzed person I helped a year ago.

    I asked him, “How are you doing now.” He said, “Sir, you recognize me not by my name but by my10state.” “With your kind help I am now able to 11 on my legs without support. I was operated 12I am married to a beautiful lady. Besides I have a good job and stable 13.

    I don't 14 remember if I gave him my phone number15 what he said next was touching. He said he wanted to return my money so that I didn't feel cheated and continue to help people 16 in the future. I don't know whether he read my facial expression the day I helped him but tears were 17 down my face. That day I18 him that I will continue to help people as I see a(n)19—small or big. It is the small event that makes a big 20 to my life.