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L1数量两个题目麻烦老师讲解一下

1。An analyst for BYG Investments Inc. is attempting to estimate the dispersion of quarterly GDP growth in the Korean economy for the last 60 years. He has collected the 240 observations of GDP growth but is unsure of the best method to visually demonstrate the dispersion of his sample data. Which of the following best shows the dispersion of a sample distribution?
A.   covariance
B.    Histograms
C.   Times series plots

2。Victor Claus CFA, is the energy analyst for Mercury Brokerage firm, Claus is evaluating a potential major new natural gas discovery of HRF Energy. A consultant hired by Mercury predicts the well will flow at 4 million cubic feet (mmcf) of natural gas per day. The consultant's prediction carries a standard deviation of 0.8 mmcf per day. What is the probability that the well will flow at greater than 5 mmcf per day?
A.   7.5%
B.    10.6%
C.   14.7%

Tanks a lot.

第一道选B,没啥好说的
第二题也选B,z=(5-4)/0.8=1.25,查z分布的表格,查出来10.6%
应该不会错的

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第一题:时间序列的散点图只能表示数据是否围绕着趋势线,不是看数据本身的离散程度,或者把它作为离散程度的衡量不是那么好,但是柱状图是一目了然的,如果比较集中,那么就反映出来某些区间内的柱比较高。
第二题:为什么要考虑n呢?4和0.8是已经经过抽样统计计算出来的数了,现在只是进行概率估计,只需要标准化之后,根据标准正态分布的概率分布来求。

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