题干

某校随机调查了110名不同性别的学生每天在校的消费情况,规定:50元以下为正常消费,大于或等于50元为非正常消费.统计后,得到如下的2×2列联表,已知在调查对象中随机抽取1人,为非正常消费的概率为 11
3
.

 

正常

非正常

合计

男

30

 

 

女

 

10

 

合计

 

 

110

(Ⅰ)请完成上面的列联表;
(Ⅱ)根据列联表的数据,能否有99%的把握认为消费情况与性别有关系?
附临界值表参考公式:

P(K2≥k0)

0.100

0.05

0.025

0.010

0.001

k0

2.706

3.841

5.024

6.635

10.828

K2=
n
(
a
d
−
b
c
)
2
(
a
+
b
)
(
c
+
d
)
(
a
+
c
)
(
b
+
d
)
,其中n=a+b+c+d.
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答案(点此获取答案解析)

解:(Ⅰ)

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    Green tree ants are important builders in the rainforest. They're like the worker bees of the ant world. The native forest of Thala Beach Nature Reserve is the natural home of these insects.

    They climb all over the tree that contains their nest and protect it from enemies with great fierceness. The ants are often in the fruiting trees of Tropical North Queensland. When an animal tries to help themselves to some tasty fruit, they find themselves attacked by a powerful, frightening army of green tree ants! Their bite is not very painful but many ants attacking at the same time can be extremely uncomfortable.

    The nests are large and constructed by sticking the leaves at the end of branches together to create a home looking roughly like a globe. Most of the nest construction and weaving is conducted at night. A mature colony of green tree ants can hold as many as 100,000 to 500,000 workers and may include as many as 12 trees and contain as any as 150 nests. Green tree ant colonies have one queen and a colony can live up to eight years.

    However, the ants are so busy that they fail to spot a dishonest figure. There is a spider called the Salticid spider, or the jumping spider, as they are sometimes referred to, which has excellent eyesight and is only active during daylight, weaving a protective covering of silk to spend the night in. Interestingly, the Salticid spider does not look like a green tree ant. Instead, it chemically copies green tree ants' smell. Effectively pretending to be an ant, it goes into the green tree ants' nest, enters the nursery and feasts on their babies. Green tree ants don't have good eyesight and smell everything with their antennae (two long thin parts on an ant's head). Therefore, the ants think the spider is another ant and ignore its presence within the nest.

    Next time, as you wander around Thala's native forest, keep an eye out for these busy little creatures. Look up into the trees and you'll likely spot their nests.

  正常 非正常 合计