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题库 / OG2017Q-PS-151
If the variables X, Y, and Z take on only the values 10, 20, 30, 40, 50, 60, or 70 with frequencies indicated by the shaded regions above, for which of the frequency
distributions is the mean equal to the median?
X only
Y only
Z only
X and Y
X and Z
还没有题目讲解（毕出老师会陆续发布对官方考题的解读，请保持关注）。
正太分布的基本性质
小心计算！
x：median=40，mean=（10+40+90+160+150+120+70）/16=40
z：median=40，mean=（40+60+60+40+100+180+280）/19=40
The frequency distributions for both X and Z are symmetric about 40, which means that both X and Z have mean = median = 40.
我蒙对答案了，能麻烦再解释下题目吗？for which of the frequency distributions is the mean equal to the median？的意思是只看frequency的mean和median吗？我算了下没有一个mean equal to median。我又用value X frequency，也还是没有一个mean equal to median。请指教，多谢多谢！
你算错了把。x和z的mean都等于median的。
x：median=40，mean=（10+40+90+160+150+120+70）/16=40
z：median=40，mean=（40+60+60+40+100+180+280）/19=40
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