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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
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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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